We have one of these near us, open all the time, a regular visiting place for my DS, and surprisingly un vandalised.
The thing I find amusing having had a nose around myself is that it has 1mtr thick walls, totally bombproof, but the comms rely on overhead BT lines on the surface - they didn't think that through!!!
The chemical lav is in a separate little room off the ladder shaft, you tip it down a grille at the bottom of the shaft and there is a hand pump to pump the waste up and out on the surface - nice!