Weird question, but are there abysses in Skyrim? I mean the "bottomless voids" found in some locations in "Oblivion", such as the Dreamworld quest where there was an obstacle course laid out over a dark void.
uesp net/wiki/Oblivion:Traps#Abyss
In Oblivion if you had a "delay death message" mod installed, you could fall in one and just go on falling endlessly in darkness, similar to when you noclip out of an interior map, then clip back on and fall away.
I tried to look for one in Skyrim but couldn't find one.

Never seen anything like that, and I explored pretty extensively. Would be cool to see though.

I seem to recall a vast bottomless expanse

Oh! Yes, that. I totally forgot about that.

There are holes in the ground, yes. That bandit camp around Whiterun, where you find the transmut-spell has one that can be explored from the inside and fallen into from the outside.

That's just a small spike pit. He means bottomless chasms of doom. You just die falling into it, since there is no bottom to hit

That isn't an endless fall either. The waterfalls under the bridge do have a bottom (there's a sea down there).