Underground Dublin, Part I: The Caves of Dublin

This is part one in a two part series, which came to fruition as a result of limited freedom of movement during the Coronavirus lockdown. It is very different to my usual articles, and its style and content may be a ‘required’ taste. For me, the cave always directs the ‘story’ and I hope that you will bear with me in what is an attempt to create something new and positive from a time of ‘speleological stagnation’. Part two deals with Dublin mines.

Dedicated to Matthew Parkes, who had the greatest of enthusiasm for even the most minor of caves and mines, and who was always eager to share his inexhaustible knowledge – as can be seen here by the many references to his work. Ní easbha go dích cáirde. Ar dheis Dé go raibh a anam.


The first thing that can be said of the caves of Dublin is that, there are no caves in Dublin. The county has small areas of granites and volcanics in the south but it is largely a limestone region. Despite the predominance of limestone there are almost no karst features or caves. Unfortunately, from a cave’s perspective, not all limestone is equal and in the case of Dublin ours is almost exclusively ‘calp’ limestone. Although similar limestones exist elsewhere in Ireland, ‘calp’ typically refers to a distinctly Dublin speciality. It describes a dark blue-ish grey, finely grained, muddy limestone formed at great oceanic depth. It has few fossils; is of brittle quality; is poor for building, and even makes substandard lime mortar.1 While calp has been used in the construction of some of our finest city buildings, its use is often confined to the buildings’ foundations. Where it is used in walls, this diminutive, even ‘ugly’ limestone, is usually invisible, being concealed beneath finer limestones or granites used in our city’s proud facades.

Calp limestone, being clay-rich and highly impure, does not respond to the dissolution processes that karstify the purer limestones of the west, forming our country’s great caves.1 In this article however, we will look at the small pockets of limestone caves that do exist in Dublin. Do not expect deep descents into vast chambers and underground networks; more-so we will descend into aspects of folk imagination which was drawn-to and animated by these natural enclosed spaces.

To note, I will not cover sea caves here. There are also a small number of mines in Dublin, and there is much crossover between mines and caves, in folk memory. Thus, this article is split into two parts, for brevity, but both parts explore many of the same themes.


Independent of the dominant calp limestone, there exists a small area of Ordovician limestones in the north of the county, between the rural towns of Portrane and Donabate. The bedrock here is typically lime rich mud layers interspaced with thick fossiliferous limestone, set down in shallow tropical seas, and displaying a wealth of fossil remnants. Of particular note here is that Portrane represents a time of Ordovician limestone, not Carboniferous, as are the limestones of Clare and Fermanagh. The Period of the Portrane bedrock predates the latter by approximately 130 million years! While the caves may have begun developing in this period, they most likely ended up looking as they do today, during the Ice Ages of the Quaternary period.2

Portrane Caves

In all, there are a half dozen caves in Portrane with a number of additional rifts and some surface karst features. The caves are very short fragments of an eroded cave system but, they are nevertheless, the best caves that Dublin has to offer! The longest is just 38 meters, while most caves are much shorter. Unfortunately this longest cave, Gloop Rift is also the most tidal and, despite being there at low tide, it was inaccessible. I visited on a Spring tide and perhaps a neap tide in the winter might allow access. Another ‘long’ cave is called Pollnagollum and it is good to see Dublin get a place on the ‘Find-a-Pollnagollum-in-every-county’ list. Pollnagollum has some interesting features. It is certainly the most cave-like in that it runs perfectly straight along an obvious joint and it has a number of decent scallops on the wall. It also has a vague phreatic tube shape, features only seen in dissolution caves. Looking back from the end of its 30m length, at the top of a small boulder climb, the cave looks and feels entirely unlike a sea cave.

Portrane Caves

The Ordovician limestone in Dublin is overlain by deep glacial deposits but, at Portrane, this has been eroded away by the sea, exposing its hidden caves. Despite their proximity to the sea, the Portrane caves are not sea caves, but solution caves. That is to say, the primary process in their origin is not the aggressive mechanical action of waves, but the slow and subtle dissolution of limestone by acidic rain, as is typical of karst caves. That is not to say the sea has no influence, indeed it continues to erode the caves, but their origin, or speleogenesis, is karstic. A keen eye inside the caves will see the subtle hints at this karstic origin, with many features more reminiscent of limestone dissolution caves rather than the dull featureless profile typical of sea caves.

Pollnagollum Cave, Portrane

Another cave, or rather, two caves which are connected, are Chink Well and Priest’s Chamber. The latter is recorded in folk memory as being a place of refuge (see below). In fact, this is easy to see why as halfway into cave the passage closes down and a second level, a few meters above, becomes the main route of the cave. I assumed I could free climb this but it was so densely covered in red algae that I could not get a firm hold anywhere. I’ve scaled all sorts of obstacles in caves but never a wall of algae! Perhaps it worked for the persecuted priests somewhat like a round tower did – a place accessible only with a ladder, which could be pulled up, once safely up! The red algae, as well as green algae present at the entrance of this cave, has caused the development of ‘photokaran’. This can be observed as a series of small limestone ‘fingers’ pointing out from the entrance. It is a result of the photosynthetic algae drawing water and nutrients from the limestone and thus disrupting the ‘natural’ flow of water through the porous rock. Being limestone, the rock responds by creating these little funnels, which then point towards the sun, the direction of growth of the photosynthetic algae.2

Similar to nearby Loughshinny mine, the Portrane caves have been the subject of folk imagination and memory into modern times. Smugglers would take their small boats out at night and, meeting with cargo ships in the open ocean, would make-away with:

“tobacco, wines, [and] spirits… The small boats would come in and sail up the caves with the goods and at the end of the caves here was a large hole going down into the cave from the top. The goods would be hauled up through the hole with a rope.”3

A number of the caves do indeed have daylight shafts at the inland end. Another folk theme common to obscure and hidden sites throughout Ireland, and which certainly echoes reality, is that of the reticent Catholic priests who gave services in such places, during Penal times. Hence, Priest’s Chamber and Chink Well cave are noted as such places:

Old people of the district say that in the penal days priests used to celebrate Mass in this cave and it was also the hiding place of these unfortunate fugitive priests. Some nearby cave[s] were also occupied by the priests but its believed that this particular cave known as the priest’s chamber was their headquarters, and it was also where they performed their religious services.4

Adjacent, Chink’s Well cave contains a fresh water spring, unpolluted by its proximity to the sea, which was “the only place they could get water for long periods at a time” to allow for mass to be held”.5 Chink’s Well takes its name from the spring which was used as a cure for Whooping cough or the ‘chinks’, as it was known locally.6  

Surrounding these two caves are another two, smaller caves. The first, named by cavers as ‘The Sacristy’, is a tight squeeze into a small chamber which is generously coated in calcite flows on its walls and floor.

The Sacristy, Portrane

The next cave, ‘The Maze’ is similarly well decorated and, at the end, features fine helictites and a large gour-pocked calcite flow. The calcite decorations are not typical of sea caves and are more readily seen in the caves of Clare and Fermanagh. Particularly curious is how these solution formed features have been smoothed out by sea wave action, giving them an unusual and shiny lustre.

The Maze, Portrane

Moving north, the caves begin to shrink in size but there are few small and interesting cave remnants as well as some exposed karst features. Overall the caves of Portrane represent the most obvious and, speleologically, most interesting in Dublin.


The Naul, An Aill in Irish, or ‘the cliff’, is a village that sits in the flat lands of north county Dublin. The name has always interested me for this reason – why, considering the topography, is it called ‘the cliff’? I was not familiar with the area but wanted to visit it, being as it is the place most associated with master of the Uilleann Pipes, Ireland’s native bagpipe, Seamus Ennis. However, I had another reason to visit An Aill, following up on J.C. Coleman’s mention of a short cave in the area.7 Naul’s dilapidated 15th century ‘Black Castle’ sits at the end of a field near the centre of the village. To my surprise it is at a cliff’s edge over a deep gorge on the river Delvin.

The Hermit’s Cave, at Naul

Scrambling carefully down the cliff, through some extremely thick scrub, one can find the cave located just below the castle. It is a beautiful spot, a green and wild canyon, something entirely hidden from landscape above. The cave itself, cloaked in a curtain of Ivy, is only three meters in length. Any hopes for a potential lockdown digging project quickly evaporated upon seeing it! I could not locate any information about the origin of the cave’s name but would be interested in hearing from anyone with a greater familiarity with it.


The final of our Dublin caves can be found within the bounds of the city itself. In the townland of Hermitage a fine crag of quality grey limestone is hidden on the wooded banks of the Liffey. Interestingly, Hermitage Cave did not typically take its name from the townland, rather the townland took its name from the cave, such is the prominence of the area’s local folkloric legend. There are many variations on this story, far too many to detail here, but they all follow the classic medieval knight and courtship tale. The story found its way into print in the 19th century, as a rhyming epic poem. In the tale, a knight and Princess court but their partnership is denied by the King. Rejected, the knight retreats to the so called ‘Hermit’s Cell’ cave in Lucan where he intends to live a reclusive and humble life. Some years later, the Princess is to be married but she flees her arranged suitor and seeks out the Hermit. She is perused by four jaunting knights but the Hermit emerge from his cave and engages in battle to the death with them. Though he kills the four knights, the Hermit is critically injured and dies. The Princess, with that predictable closure of Irish folklore, also dies. From the bodies of the Knights spring five lime trees and a single whitethorn would grow at the Princess’s place of death. The lime trees still grow at what is now Hermitage Golf Club, but the whitethorn sadly died, within living memory. In other variations of the story, the knight did not initially retreat to the cave but rather survived combat and, feeling shame for his actions, became a hermit to atone.8

Exposed limestone crag at Lucan

As typical or cliché as this story seems it is, in fact, most unusual. Jaunting knights and maidens are not the stuff of Irish mythology, nor its folklore. However, remove the medieval guise, and the story is in essence that of the Fennian mythological cycle of ‘The Pursuit of Diarmuid and Grainne‘; and it is further likewise similar to the Ulster Cycle’s ‘Deirdre of the Sorrows‘. These stories, in themselves, are believed to have been the basis of the European medieval tale of ‘Tristan and Iseult‘. The latter story, featuring knights and maidens, and having many connections to Dublin, loaned its name to Chapelizod (Séipéal Iosóid, or “Iseult’s Chapel”), a village just a few kilometres east of the cave!9 This recycling and redevelopment of stories in the popular imagination is fascinating and, just like caves, trying to find their connections, their origins and their purpose gives an incredible insight into the constant yet ephemeral story of the natural and human landscapes in which we live.

The area where Hermitage Cave is located, while not extensive, is truly beautiful and it is not what one might expect to find within the city. There are two small caves and it is difficult to know which one is the named ‘Hermit’s Cell’. The bigger cave, to the east, is three or four meters in length and has all the hallmarks of a limestone cave, except that it doesn’t go anywhere! The smaller cave, which is really only a meter long, is certainly the less shelter-like of the two. However, I would suggest this less comfortable one is the cave which folk memory calls the ‘Hermit’s Cell’. This is perhaps best explained by looking at it, with its neat square shapes and door-like entrance, it might be easily have been understood as a manmade cell.

other caves

The caves mentioned thus far are recorded both in topographical records and in our folkloric records. In Dublin, however, there are a number of caves which exist in reality, but not in folklore. There are also caves which exist in folklore, but not in reality. An example of the former is in Newcastle, a village in south Dublin, with a long history of medieval settlement. Approximately 15 meters below the town and running to the west for at least two kilometres is the ‘Newcastle Buried Channel‘. This is an enormous cave passage which represents a gravel in-filled Vauclusian spring cave. That is, a spring which originates from a cave passage and in which the water is forced upwards, under great pressure. Shannon Pot, in Cavan, is similar albeit a much smaller and inferior example of a Vauclusian spring (L. Brown, personal communication, 14/06/21). The chamber in Newcastle is in parts 100 meters wide by 100 meters deep. Unfortunately for us cavers, it is inaccessible, being buried beneath glacial till and it has only been described by data retrieved from borehole logs.10

In 1997 Parkgate Street, in the city centre, at a site undergoing archaeological excavation, a short tunnel was discovered. This was found to be two meters wide and up to three meters high. It was finely decorated with calcite and most unusually, was more of a cavity in glacial till, rather than a cave in limestone. A stalactite was dated to 1,500 years before present and it is assumed the cave was formed as a result of re-advancing glaciers.11 This cave, first noted by Matthew Parkes, has been recently revisted and there will be an article published on it, shortly. The cave is now named Sadler’s Cave (G. Ll. Jones, personal communication, 05/07/21). Such features most likely riddle Dublin and other parts of the country but it is extremely rare that we get a chance insight.

Portrane Caves

An example of a cave which exists in the folk mind but of which nothing is known physically, can be given for the village of Lusk. We have three common words in Irish for cave; they are póll (such as Pollnagollum), uaimh (Oweynagat) and pluais (Pluais Sciathan Leabhair). The village of Lusk, however, derives its name from ‘lusca‘ an Irish word, or possible an Old Irish word, for cave. This is supported by a folkloric story which states:

St. Macculinn is the patron saint of Lusk. He lived in a cave near the Round Tower and that is how Lusk got its name, “lusca” meaning a cave.12

Other folk stories tell of how the Saint was buried in a ‘lusca’, which means variously ‘cave’, “underground chamber, vault or crypt”.13 Beyond the story I know of no caves in the region, and the idea of there being one in the village seems unlikely. While folk memory may on occasion alter reality significantly, it is unusual for such a story to refer to something in the landscape which is not visible. So, perhaps there is a cave buried beneath the rubble of an older church but, we will probably never know.

Folk memory further recounts that even in the granite hills of Ticknock in south county Dublin there are ‘caves’. Soldier’s Cave, apparently contains large chambers loaded with the spoils of an unnamed war. Of this cave “people say at night there is a man with half of his body, and half of his left arm, with a lamp in his right hand guarding the entrance, so that nobody would rob anything belonging to them.”14

Though Dublin is lacking in many caves, the draw of these environments on the imagination seems so great that people have constructed their own caves. Sometimes this is manifested in stories and fiction but, in some unusual cases, people have actually built caves. In St. Anne’s Park on the northside and St. Enda’s Park on the southside can be found in each, a cave folly.

These are Romantic 19th century cave replicas built simply to provoke ideals of natural and cultural heritage for the increasingly industrialised city population. While no grandiose works, they perform the same purpose as the generations of story tellers, and all are testament to the power that the underground has on the imagination of people.

Part II of this article ‘Underground Dublin, Part II: The Mines of Dublin’ is available here[coming soon!].

Portrane Caves


1Hennessy, R., Meehan, R., Parkes, M., Gallagher, V., and Gatley, S., 2014, The Geological Heritage of South Dublin County: An audit of County Geological Sites in South Dublin County. Dublin: Heritage Council.

2Simms, J., Parkes, M., and Jones, G., 1991, ‘The caves and karst of Portrane, Co. Dublin’, Irish Speleology, 14, pp. 40-51.

3Kinsella, F., 1936, ‘The Smuggling Caves of Portrane’, The Schools’ Collection, 0789 pp. 277-278, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4498569/4385005 on 12/05/21].

4Byrne, T., 1936, ‘The Priest’s Chamber’, The Schools’ Collection, 0789 p. 271, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4498569/4384999/4498574?ChapterID=4498569 on 12/05/21].

5Gargan, M., 1936, ‘The Chink Well’, The Schools’ Collection, 0789 p. 267, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4498569/4384994 on 12/05/21].

6Bates, J., 1936, ‘Donabate and Portrane’, The Schools’ Collection, 0789, p. 317, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4498592/4385050 on 19/05/21].

7Coleman, J.C., 1965, The Caves of Ireland. Anvil Books: Tralee.

8Greene, J., 1938, ‘The Hermitage Cave’, The Schools’ Collection, 0794 pp. 280-288, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4498569/4385005 on 02/07/21].

9Campion, M., 1938, ‘The Five Knights’, The Schools’ Collection, 0793 pp. 172 – 181, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4428212/4386146 on 31/05/21].

10Jones, G. and Drew, D., 2015, ‘The Buried Pre-Glacial Channel at Newcastle, Co. South Dublin’, Irish Journal of Earth Sciences, 33, pp. 77-74.

11Meehan, R., and Parkes, M., 1997, ‘A small cave within Quaternary deposits at Parkgate Street, Dublin 8’, Irish Speleology, 16, pp. 44-45.

12Devine, M., 1937, ‘My Home District’, The Schools’ Collection, 0786 p. 229, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4498394/4384214 on 01/06/21].

13Ó’ Mianáin, P., 2020, Concise English–Irish Dictionary. Dublin: An Gúm

14Tracey, A., 1934, ‘Hidden Treasure’, The Schools’ Collection, 0797 p. 108, Duchas.ie. [Available at: https://www.duchas.ie/en/cbes/4428232/4387331 on 01/06/21].

Caves By County