Dunmore Cave is as famous for its history as for its beautiful calcite formations, and has yielded many archaeological treasures. Admission is via a compulsory guided tour that leads down a steep descent to caverns full of stalactites, stalagmites and columns, including the 7m-tall Market Cross, Europe's largest free-standing stalagmite. There are 700 steps in all. Although well lit and spacious, it's damp and cold; bring warm clothes. It's 11km north of Kilkenny city, signposted off the N78.
In 928 marauding Vikings slaughtered 1000 people at two ring forts near the cave. When survivors hid in the caverns, the Vikings tried to smoke them out by lighting fires at the entrance. It's thought that they then dragged off the men as slaves and left the women and children to suffocate. Excavations in 1973 uncovered the skeletons of at least 44 people, mostly women and children. They also found coins dating from the 10th century. One theory suggests that the coins were dropped by the Vikings (who often carried them under the arms, secured with wax) while engaged in the slaughter. However, there are few marks of violence on the skeletons, lending weight to the theory that suffocation was the cause of death.