A maze of little twisting passages, all alike.
To any americans (or indeed others) who may not know, in the UK the floor at ground level is the ground floor, i.e. floor number 0, and the one above that is the first floor. However, in JCMB, you could jump from the second floor without getting hurt, though you'd look a little silly - the numbering starts with one floor below ground level being level one.
That's not my point though. There are two first floors. You walk along the second floor corridor, and signs 'Floor 1' and 'Other Floor 1'. They are on the same floor though. But not joined except via the second floor. And one of the first floors' stairs are right in the middle of the second floor. Which is fun to go look for.
And as for the vulcan nerve pinch that apparently has to be applied to the lift buttons occasionaly to make it work - I wouldn't know, I'm not experienced enough in the lore of JCMB to do more than watch other JCMB-goers do it. And wonder.