Not strictly that far underground but in a cellar two storeys down , in quite a sensitive part of Manchester lies this old lets call it an air-con unit that had a dual purpose , one to keep the building upstairs vented and two the other extractor disappeared into the floor and all the entrances to where had been well and truly sealed...but it is worth showing the pic,s as it is very untouched..
Through the door and "WOW"
Sorry the pics are crap , no tripod
This was the air filter...
And the fan with person to show scale...
Whoops was that the on switch !!
Now we never did find out where the vent went
but it would be nice to think here.
Its nice to find time capsules like this one.....