So russian at the time it was built (those 50 years ago)?

Chinese?

yup

nope; big (dead giveaway?) I wish I was in one during this miserable impending heatwave today!:wah:

A cooling reactor?

I think I'm outta ideas :doh:

Some kind of refrigeration plant?

Hmm, Aktung said something about "nuclear" context, and "electromagnetic" :hmmm:

Reactor cooling system?

it undoubtedly had cooling and heat facilities to house the crew

Only in the sense of the nuclear era ie Cold War and any number of electro magnetic devices to accommodate communications and atmosphere mixology transfer valves for crew habitation/breathing; generally under pressure...which on occasion proved mortal. Eichhörnchen got the name half right in post 725!

Some .. device to build Chernobyl, like construct a basement underwater, like a caisson?

exactly, in fact "caisson disease" was a major issue; costing lives in on accidental surfacing. Now 4 the name...which Eich has already partially broached inadvertantly but abley...

Chernomor II undersea lab

It is indeed! Eich takes it!:salute: https://www.subsim.com/radioroom/picture...ictureid=12703 https://medium.com/predict/historica...b-3e84ece61c92

Congratulations to Eichhörnchen :salute:
This was a nice one and a fascinating read in this link, have never seen nor heard of this. Sealab and Cousteau's yes, but not Chernomor.
(Sealab III also seems to have become a disaster: https://en.wikipedia.org/wiki/SEALAB)

Thanks, Kai - when it became apparent that this was some kind of undersea (perhaps polar) dwelling, I added my previous 'half correct' answer into a search for "underwater habitation cher"

A very difficult one so well done, Aktung



https://i.imgur.com/Eh7kHbe.jpg Now where would you have seen this?