BBC News website reader Lewis Bush has been inside a nuclear fallout shelter in Lucerne, Switzerland. Here we present his pictures and accompanying captions.
In the event of a nuclear strike, anyone seeking shelter in the bunker would have been decontaminated. Cold water would have been used to wash off radioactive particles.
Two main corridors connect every room in the bunker and serve to carry the sinister echoes that ring around the complex even when it is empty.
Each civilian dormitory was designed to house 200 people, but could take double that. Most people would have been unable to move around freely.
Military accommodation would have been marginally better, but still cramped and uncomfortable.
Washing facilities were basic, with the only showers reserved for decontamination.
Everything needed to survive was kept in the shelter, from ropes and winches to bicycles - the latter to be used mainly by military personnel for scouting on the surface.
A massive store of air-tight sealable buckets were also kept in storage, to be used in the event of the toilet system breaking down.
All air entering the shelter would have had to pass through a series of disposable filters to remove radioactive material.
So important was the water filtration system that it was designed to be as simple as possible, so that even people with very limited experience would have been able to maintain it.
My view of photography is that it's important to take photos of things most people will never see, but which have a wider significance. This shelter was one such thing.