Typical County Fermanagh stream passage in Marble Arch Caves. At 11.5 km (7.1 mi), the system is the longest in Northern Ireland and second longest in Ireland.
The deepest cave in Ireland is Reyfad Pot in County Fermanagh, Northern Ireland, 193 metres (633 ft) deep.
The longest cave system in Ireland is Pollnagollum–Poulelva in County Clare, Republic of Ireland, with at least 16 kilometres (9.9 mi) of passageways.