Goblins V: It's Hard-Kore!

[Seerow]

It's equivalent to a Compacting Room trap, so XP for a CR 6 encounter.

I dunno, the details of that trap include only a 12d6 crush attack (this seems to be a bit more lethal than that), and I'd argue the hidden switch bypass here is worth a CR boost because of the way it works ("Oh hey, I found the switch! Crap now the switch is gone!")

I'd say those details boost it from CR6 up to a CR8 or 9 at least.