Dunmore Cave is located in an isolated limestone outcrop on the Castlecomer plateau, overlooking the Dinin River valley some seven miles to the north of Kilkenny city.
The areas in Ireland in which caves are most abundant include the Burren of Co. Clare, the Marble Arch area of Co. Fermanagh and the uplands of Co. Leitrim and Co. Sligo. All these areas, and Dunmore, are formed of Carboniferous limestone, laid down over 300 million years ago. Part of the interest of Dunmore Cave stems from the fact that it is the only cave of significance known in south-east Ireland and its nearest rival in size is the Mitchelstown Cave in Co. Tipperary some fifty miles away.
The largest Irish cave so far discovered, Pollnagollum, Co. Clare is over seven miles long and the deepest is over 150 metres below the surface. By contrast, Dunmore Cave contains less than a quarter of a mile of passages and its deepest point is only some 50 metres below the entrance. Yet, despite its modest size, the beauty of its formations and its scientific and historical interest make it one of Ireland's most fascinating caverns.
The cave, with its imposing entrance, has been known for centuries but it is only comparatively recently that it has been fully explored and attempts have been made to unravel its history. Until the seventeenth century caves were regarded with dread and awe as being entrances to Hell, and to this day caves are still objects of mystery and fear for many people. From the eighteenth century onwards a number of visitors, including scientists and historians, have written about the cave.
Dunmore cave is, since 1940, in the care of the Commissioners of Public Works as a National Monument because of its historic interest. Research on geological and historical aspects of the cave has been pursued making it one of the best documented cave sites in Europe. In 1967 a Development Committee for the cave was formed, largely through the enthusiasm of the late J.C. Coleman and as a result a visitor centre and site museum was built and the cave surroundings were landscaped. Stairs and walkways and an extensive lighting system were installed inside the cave thus enabling its main features to be viewed by the general public without any need to engage in pot holing.
Dunmore Cave consists of a series of chambers connected by short lengths of narrower passageway. The names assigned to the principal chambers in recent literature differ from those which are believed to have been in general use locally in earlier times. The traditional names are used here.
Most of the cave is horizontal with its roof Iying some 10-15 metres beneath the land surface above, but two of the larger chambers (Main Hall and Crystal Hall) lie at a lower level than the rest of the cave. The impressive entrance, 12 metres wide and 6 metres high lies at the foot of a natural amphitheatre of limestone up to 20 metres in height and the steep slope into the cave is largely made up of boulders which have fallen from this cliff. This slo pe shows an interesting zonation of vegetation due to the great changes in environment which occur within a short horizontal distance. Plant life in and around a cave is restricted, primarily by the lack of light, and only species which can overcome this handicap will survive. At the head of the slope are found the common flowering plants of the area but downslope these are gradually replaced by ferns, then by liverworts and then by green algae on the rocks. Within the entrance itself only a few algae and fungi are present. The interior of the cave is virtually devoid of plant life although in several places a white fungus has sprung up, obtaining its nourishment from spots of candle grease left by visitors.
None of the insects or water life in the cave are indigenous (troglodytes), they have simply found their way in from the surface and managed to survive. At one time the cave supported a large bat colony and bat skeletons encrusted with calcite flowstone have been found; but nowadays bats are only to be found in the remoter recesses of the cave.
The section of the cave extending from the entrance arch to the foot of the steps is known as the Main Hall. The huge boulders littering the floor of this chamber have fallen from the roof above, thereby enlarging the cavity. The steps end just above the Fairies Floor and immediately overhead is a fine example of a calcite cascade formation developed over thousands of years by water seeping out of a narrow fissure in the rock and depositing crystals of the mineral calcite. The Side Hall, halfway up the stairs, is simply the upper level continuation of the Main Hall and has a floor of boulders. The roof here is completely horizontal and consists of a black sparry limestone interlaced with white veins of calcite. The wall of this chamber furthest from the entrance is completely covered in calcite deposits ranging in colour from pure white to reddish (iron staining) to black (manganese staining). The water that is laying down this deposit seeps out of a major, vertical north-south fissure in the rock which runs almost the entire length of the cave.
To the north (left) the passage contracts and the roof is richly decorated with numerous straw stalactites. These fragile structures only 6 millimetres in diameter and 7-25 centimetres long are formed at the point on the roof where a small drip of water falls to the ground.
Above the stairs the passage enlarges considerably at the entrance to the Cathedral. Again the floor is covered in boulders but in this area they are covered with a thin layer of calcite which indicates that a long period has elapsed since they fell from the roof. There are fewer straws in this area as most of the seepage water from the surface above enters via fewer but larger fissures to form big stalactites or stalagmites. The Cathedral proper is about 10 metres high with a cone of boulders forming the floor. Collapse is very active in this area due to the presence of a major line of weakness in the roof. To the north of this chamber the limestone strata are no longer horizontal but are tilted to the north.
Beyond the Cathedral is the Rabbit Burrow, a rectangular shaped passage 12 metres high and 4.5 metres wide with a floor of soft sand and gravel. These deposits were laid down by the stream which originally flowed in the cave and within a few hundred feet they completely fill the passage and prevent any further progress.
Just before the climb up the boulders of the Cathedral, a narrow passage between boulders in the floor leads to one of the most recently discovered sections of the cave, the Crystal Hall. Because of difficulty of access this section of the cave is not open to the general public. This is a large chamber with a steeply sloping floor leading down to a small lake in which the water is usually perfectly clear with a blueish tinge. The water level in this lake rises and falls seasonally by up to 15 metres vertically and it corresponds to the local level of saturation in the rock. Crystal Hall is the most beautiful part of the cave being adorned with every kind of calcite formation.
Returning to the Side Hall, the tour route continues up the spiral staircase and along into a very large rift chamber (over 15 metres in height) the roof of which is only just below the surface, before entering the Town Hall. This chamber is again the product of roof collapse along the line of weakness in the rock. The centre of the chamber contains a fine series of calcite pillars of which the Market Cross is the largest (over 5 metres high and 1.3 metres in diameter). These columns originated as water seeping in from the fissures above deposited calcite both on the roof and floor of the chamber, the two deposits eventually growing to meet one another and form a pillar. The calcite deposits in this chamber are very pure as indicated by their whiteness. Floor deposits dominate the Town Hall as the seepage water enters this cavern in dribbles rather than as single droplets thus allowing little time for deposition to occur on the roof.
Although Dunmore Cave is now 'fossil' in the sense that is has no stream, there is much water present, chiefly derived from seepages of rainwater from the surface. This water enters the cave at many points especially following heavy rain and the Cathedral, the Town Hall and the top of Crystal Hall being close to the surface have particularly heavy drips. It is these waters that keep the calcite formations alive and growing.Caves usually maintain a very constant temperature throughout the year in the zone away from the entrance. This temperature will correspond to the average annual temperature for the region in which the cave is located. In the more distant parts of Dunmore the temperature is always between 8 and 10 Degrees Celcius whilst the water remains at 9 Degrees Celcius. This is because the cave air and water takes its temperature from the surrounding body of rock which is scarcely affected by seasonal changes of temperature for more than a few feet below the surface. Air within the cave only varies by 2 degrees Celcius between summer and winter, whereas on the surface above the seasonal contrast can be as much as 30 Degrees Celcius. The cave air is always completely or nearly saturated with water Vapour gas (as indicated by breath condensing)- hence the perpetual dampness of much of the cave.