...that could serve as a PORTAL
to a parallel universe.
The Big Bang Theory Season 6, Episode 8
You went out in the hallway,
stumbled into a PORTAL...
The Big Bang Theory Season 4, Episode 9
Newspapers? Did you find
a PORTAL back to the 1990s?
The Big Bang Theory Season 11, Episode 13
It's just a PORTAL to hell.
The Big Bang Theory Season 12, Episode 9