That's a whopper.
When I was a teenager, we had a 'den' in an icehouse on one of the big country estates where a friend lived, but that one was probably only about 10 feet diameter, and 8ft deep (it would have been deeper originally, but the base was covered in broken bricks where the roof had collapsed). I'm sure there was a more complete one in the area, but I can't remember where that was.