Dunmore Cave, Show cave and national monument in Castlecomer, Ireland.

Dunmore Cave is a limestone solutional cave in the Clogrenan Formation, cut into an isolated outcrop on the Castlecomer Plateau above the River Dinan valley. Its passages run about a quarter of a mile and reach 46 m deep. The Market Cross, a cross-shaped calcite column over 5.8 m high, is the best-known formation; the photograph shows a rounded stalagmite with ridged, drip-draped sides and a flat cap.

Historical records mention an event in 928 AD when a major raid caused heavy casualties. This episode shaped the site's importance in medieval Irish annals.

The name Dunmore comes from the Irish 'Dún Mór', meaning great fort, and appears in ancient texts as one of Ireland's three darkest places. Visitors sense this connection to early Irish culture as they descend into the dark chambers.

Tours follow a quarter mile of passages down to 46 m, with steps and uneven, damp ground underfoot. The visitor centre at the Mohill entrance sits off the N78, about 11 km north of Kilkenny City. The cave stays cold year-round, so wear warm layers and sturdy shoes.

During excavations in 1999, a rare collection of 43 silver and bronze objects from around 970 was discovered in the deeper reaches of the cave. This find provides insight into earlier human activity at this mysterious location.