When you're it feels pretty big. Other factors that contribute to the vastness are...
- the local map doesn't fit on one screen
- its dark!
- the height range of the terrain is pretty varied

Eh, I just had the impression that it was a massive dungeon complex with tons of loot, enemies, and the like, but really it's just massive open ground/underground with only a few actual small dungeons/rooms. I mean, it's neat visually, but it's definitely not a super-massive dungeon. In fact, there's very little fighting to be had. I think the Dwemer ruins in Markarth are the largest dungeon in the game, but then again, several locations in the game are fairly large.

I agree with the thought that it was a cool zone (BR) but smaller than I expected based on whsg people had been saying. I arrived, cleared it, cleared all 12 auxillary rooms/zones, and found 34 crimson nirnroot, all in one session.

Neat, awesome, but not big really.

Come on guys... i'm looking for the bizarre to keep me trudging along my delving ways.

Promise me there's a old working DK arcade game (circa 1981) waiting for me somewhere in the rift.

Or the only hourglass in the game is thirteen stories tall and is under winterhold.

I have a feeling things like these are random.... the RNG wins - EVERY time.

That would be where the previous poster saw the underground dragon....

Is it a bit sad that I used to collect hourglasses in Oblivion as if they were trophies? I want a thirteen story tall hourglass under Winterhold!!!!

Most of these set pieces i believe are structured. Events in them might be procedural but...

I think that not knowing where exactly is better though. Gives the sense of "An under ground dragon? No way. Maybe i should clear out the rest of the Rift. I only got what? five more places to check..."

Also today i found:

One giant spinning orb, looking ebony in nature.
A pack of non-hostile vampires.
A Skooma den basking in glowing mushrooms.
Two Draughs standing nose to nose having a "conversation" (?)

A family that was having suspicions of a skeever infestation, only to be dragged to their doom by a Falmer legion living just below. The eventual skinless half of a head at the bottom was the perfect touch.

Perhaps this would not have happened had they not been enslaved by the Dwemer and forcibly develutionized by the raw truthiness and power of glowing mushroom poisoning.

hmm.. the glowing mushrooms, they give sight and they taketh.