Marble Arch Caves

Water draining off the slopes of Cuilcagh Mountain sinks into limestone and reappears here, and the caves are what that process has hollowed out over hundreds of thousands of years. Tours are guided only and start, when water levels allow, with a short boat trip along an underground river into the system - an unusual opening that most show caves cannot offer. Beyond the landing, walkways lead through chambers with stalactites, curtain formations and calcite flows, past a junction where two streams meet. Above ground the site sits within a Global Geopark that crosses the border into County Cavan, and the boardwalk to the Cuilcagh Mountain viewpoint, a long staircase of steps up the escarpment nicknamed the stairway to heaven, starts a short drive away across blanket bog.

What you actually see

• The underground boat trip - the entry along a subterranean river.
• Calcite formations - stalactites, curtains and flowstone in the chambers.
• The stream junction chamber - where two underground rivers meet.
• The Cuilcagh boardwalk - a stepped path over blanket bog to an escarpment edge.

When to go

May to September, when the caves keep their fullest opening hours and the boat section is most likely to run. Tours must be booked and sell out in school holidays. The cave holds a constant cool temperature of around 9 degrees, so bring a layer whatever the weather outside.

Honest expectations

Heavy rain raises water levels and closes the caves entirely, sometimes at short notice, and the boat section is dropped first - phone ahead on wet days. Tours are fixed-pace with a group, so photography time is limited. Footing is wet and there are steps throughout. The Cuilcagh boardwalk is a separate site with its own steep climb and busy car park.

Nearby

Lough Erne and Enniskillen lie north, and the Cuilcagh boardwalk is a short drive away.