A hatch in the middle of moorland leads down to a short entrance passage, which then drop down into a larger room.
 
The main room was a backup receiving area for the Chain Home radar station during the second world war, I am omitting the exact location on purpose as its filthy and flooded to the ceiling and you’ll only end up getting as wet as I did or worse.
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I have seen the hatch but never looked underneath. WIth it being a peat moor I assumed it would be full to the rim after more than 60 years
its the receiver buried reserve at danby beacon at a guess (the transmitter being under a couple of tons of earth near the beacon),it was sealed up when i saw it.Been in several BRs and most are flooded to waist high with various hazards