At 1,375 feet below ground of the Snowdonia mountains in Wales, adventurous explorers can get the world’s deepest sleep.

Though often called ‘the world’s deepest hotel,’ Deep Sleep clarifies on its website that it is neither a hotel nor a bed and breakfast. Instead, visitors are in for an overnight “remote-camp adventure experience” inside the world’s “largest and deepest abandoned slate mine.”

A chance at staying overnight occurs once a week, from Saturday evening through Sunday morning. The site has four log cabins with two twin-sized beds in each one. There’s also a “grotto” accommodation with one double bed. While a compost-style toilet is available, there are no showers. Staying at the grotto will likely be a silent oasis besides your own chatter and noise. Contrastingly, you’ll be more likely to hear dripping or even running water nearby in the other accommodations.

Guests have access to lab-tested running water via a spring at the mine. There’s Wi-Fi, but likely no cell reception for making calls via your provider. Bedding and an “expedition-style” dinner, breakfast items, and beverages during designated meal times are provided. Additionally, visitors can bring their own food and drinks.

How Much Does A One-Night Stay Cost?

A Deep Sleep cabin costs £399 (around $512) per night, and £599 (around $769) per night in the grotto. Each stay welcomes up to 2 guests per booking. The price remains the same even if you embark on a solo camping experience.

What Else Should I Know About Staying At Deep Sleep?

Bookings must be made in advance. Visiting Deep Sleep is an experience moderately fit people may enjoy most – as the two-hour journey to and from the site requires hiking, balancing one’s weight, ducking, and other abilities. A Deep Sleep trip leader will guide you to and from the slate mine, as well as provide the necessary equipment and boots you’ll need. Visitors must pack light for their stay, as it’s best to fit one’s overnight essentials into a backpack for an easier trek. Having layering pieces is a good idea, as some may find the temps chilly in the mine.

Smoking and drinking on site are prohibited.

Though the United Kingdom’s mines and caves are usually humid, dehumidifiers run when the Deep Sleep accommadations aren’t occupied so they should be dry when you arrive.

Can You Visit Without Staying Overnight?

Deep Sleep is an overnight experience. However, the operator behind it, Go Below, offers various underground activities for exploring and enjoying Snowdonia’s underground. The opportunities include zip-lining, boating on underground lakes, climbing, and more.