Cave & Underground
Deep Sleep, Snowdonia
Wales
Bunks 419m down a slate mine — deepest hotel claim
Four twin cabins and a double 'grotto' behind a steel door 1,375 feet down the abandoned Cwmorthin slate mine — the deepest overnight accommodation on Earth, reached by a steep hike and then a two-hour guided descent past miners' stairways and decaying bridges. Dinner is an expedition-style meal in the 10°C chamber, and when the lamps go out the darkness is absolute. The catch: Getting to bed is a graded caving trip — a steep 30-minute hike plus ~2 hours of ladders, bridges and scrambles (age 14+), it typically runs only one Saturday night a week, and there are no showers.