"Wally" spaketh thusly. . .
JG wrote:

Whenever he shows up, he usually
bonks his head on a beam on the ceiling... sort of transition between
two rooms.

Over here, we call that 'a doorway'.

In the gay bath house Jonathan Ganz frequents and is referring to,
Binary Bill, a welcomed guest, says it's called an 'alcove.'

I hope this helps.

CN