Blackreach

Underneath Frostflow Llighthouse-first time facing Falmer and Chaurus

Avanchnzel- interesting side story

Hillgrund's Tomb- went here for the first time at level 50 (had to keep the person safe and there were 4 Deathlords at a time in a couple of the chambers).

Underneath Frostflow Llighthouse-first time facing Falmer and Chaurus

that one was awesome as well.

Same here, that was epic as *poop*! I lost my first follower in there... She was bait for me to run out as fast as I could after killing that giant monstrosity!

-Frostflow Lighthouse! That showcased what most dungeons should be like. The story behind all of it was amazing and going to the lighthouse for the reward was awesome too.

-All of the Dwemer Ruins, especially Irkngthand and Avanchnzel

Bleak Falls Barrow because I've done it way too many freaking times to count. And I hate it.

blackreach was awesome, the bloated mans cave during hircines quest is very nice too

I'd say all the Dwemer ruins, because I'll see them again in my nightmares.
Now, seriously, my favorite dungeons are probably Blackreach (that place is HUGE) or Labyrinthian (greatest adventure time I've ever had).

I like the ones with a chasm and you have to leap down from ledge to ledge with no way back up except to keep going forward, like the Sightless Pit and that dwemer ruin near Winterhold ruin that leads to Blackreach.

Some of the caves are great. There is one near Markarth with a huge toppled tower inside which is pretty cool, and another near Solitude with pirate ships trapped during a cave-in.

Black reach, something about it with the glowing mushrooms and epic scenery is just awesome. DO NOT HURRY while in Black in reach, I missed aton of loot,armor,weapons when I was in a hurry since I was on the main quest. Difficulty is about 5.5/10 with Ebony weapons and armor, also with Difficulty on apprentice/normal.

Yeah this one! Haven't seen Blackreach of Labyrynthian yet though. shadowgreen is amazing.

Well guys i can tell that playing in master any dungeon can turn into ur subterranean grave...for sure its a complete way to play the game u are more careful and always be in the look out..but as i read above any dwemer/falmer dungeon its pretty epic for me...since the amount of enemies u have to face ....

Frostflow Lighthouse - Man oh man I was so scared. Great story, too.

Bloated Man's Grotto - great visual

And that cave where you go to for the Orc stronghold's Daedric quest (I don't remember the name)

I haven't been to Blackreach yet unfortunately...

Blackreach - I waited quite a while to do the main quest. To think I had sunk a couple hundred hours into the game THEN get treated to something so surprising and visually inspiring. Very memorable.

Northwatch Keep - Not because its a particularly memorable location on its own, but because my sneaky character assassinated every Thalmor soldier inside and outside without the slightest hint of detection. Not even the last Thalmor suspected anything was wrong.

Labryinthian - Memorable boss fight, unique weapons, neat (if simple) magic based puzzles, and that ancient evil voice that keeps talking to you throughout

My favorite cave is Stoney Creek Cave. It just looks cool inside to me. I would love to be able to claim it for my "house".

Blackreach, obviously. Second to that, probably Frostflow Lighthouse.

I had to think a while.... I bet I've been in every dungeon at least once by now.

Labyrinthian.... I LOVE that place.

Blackreach - it's very very cool, even though I have a hell of a time seeing in there due to the "blueglowy" lighting.

Shadowgreen - it's not large but it is extremely gorgeous. Not to mention if you aren't "on your game" you will be dead pretty shortly.