Talk about a deep sleep. A hotel that claims to be the deepest in the world has opened 1,375ft below the mountains of Snowdonia in Wales. This subterranean bolthole, with stays costing up to £550, is set deep within a chamber of the abandoned Cwmorthin slate mine and can only be accessed via a ‘steep and challenging’ route through the old workings. Called ‘Deep Sleep’, it’s comprised of four private twin-bed cabins and a ‘romantic’ grotto room with a double bed, a dining area and loo facilities with simple toilets and sinks. The hotel, which describes itself as a ‘remote-camp adventure experience’ and is run by the outdoor activity company Go Below, only opens one night a week – Saturday night. Guests’ experience begins on Saturday evening at 5pm at Go Below’s base near the town of Blaenau Ffestiniog, where they meet the guides that will lead them to the hotel. First, they must trek 45 minutes into the mountains on a route that’s ‘steep at times’ but said to offer ‘beautiful’ views. They stop at a cottage to ‘kit up’ for their descent into the netherworld with a helmet, a light, a harness and Wellington boots. What’s next? The hotel website says: ‘Then it’s time to say goodbye to the outside world and head into the depths of the world’s largest and deepest abandoned slate mine.’ Tackling the challenging route through the mine – which was worked from around 1810 to 1939 – guests will navigate ancient miners’ stairways, decaying bridges and scrambles. The guide will provide ‘plenty of historical information’ about the lives of the men and boys who worked in the mine en route, with the descent to the hotel taking around an hour. When they arrive at Deep Sleep – its entrance marked by a large steel door – guests are welcomed with a warm drink and can enjoy a complimentary ‘expedition-style’ meal on the hotel’s picnic table. ‘Then you are welcome to retire to your bed for a very deep sleep,’ the hotel notes. Year-round, the hotel sits at a temperature of 10 degrees Celsius, but the cabins are ‘quite cosy’ thanks to the thick insulation that lines their walls. All electric lighting is low-voltage and powered by 12v batteries. Surprisingly, it does have Wi-Fi, provided through a one-kilometre-long ethernet cable from a 4G antenna on the surface. There’s even running water from a spring within the mine. The guide and a member of technical staff stay overnight in the hotel, with breakfast – ‘simple snacks’ and a warm drink – taking place at 8am the following morning. Then, it’s time to make the ascent to the surface of the mine, reaching daylight once again. The idea for the experience, which launched in April, came from Go Below’s founder, Miles Moulding. It takes the crown of the world’s deepest accommodation from a hotel suite that lies 508ft underground in Sweden’s Sala Silver Mine. A private cabin for two is £350 and a night’s stay for two in the grotto is £550.