Stairwell.
The Big Bang Theory Season 3, Episode 2
Don't look down if you're subject
to vertigo... and use their STAIRWELL.
The Big Bang Theory Season 1, Episode 14
Why are you sitting
in the STAIRWELL?
The Big Bang Theory Season 7, Episode 13
The door to the STAIRWELL
of the other building was locked.
The Big Bang Theory Season 1, Episode 14