Submarine rescue chamber.
https://diqn32j8nouaz.cloudfront.net...ue_chamber.jpg
https://diqn32j8nouaz.cloudfront.net...e_chamber1.jpg
Previously:
https://www.homemadetools.net/forum/...812#post152362
https://www.homemadetools.net/forum/...911#post144589
https://www.homemadetools.net/forum/...369#post150720
https://www.homemadetools.net/forum/...018#post145055