Favorite Instance is Karazhan.
Definitly Ulduar, its huge, the visuals are great, the bosses are unique, and the lore scenes when your at the last boss are fun to see.
My favorite instance is Scholomance hands down i think its such a fun one to run!
Icecrown Citadel. The Plagueworks made that raid for me. A lot of fond memories with my guild at the time as well.
Blackrock Foundry is my favorite because it provides a challange and accually takes skill to get through
My favorite instance is Karazhan
Favorite instance? Probably Karazhan. First raid I participated in. The atmosphere and design were amazing.
My favorite Instance is Utgarde Keep
Favorite instance would have to be Shadowfang Keep for dungeons... Close tie between ICC and Karazhan for raids
Favorite instance since I started playing WoW has to be Scholomance! I love the look and feel to it.. I remember doing the quest chain to be able to enter the instance.. Or pulling the rare spawn to the meeting stone (sorry people that were AFK there). Or doing Paladin class quest to get your Charger mount.
Old Deadmines, the first ever instance that I did with friends back in BC on my first character, took us half an hour to find the entrance, but it was probably my favourite experience in WoW :D
My favorite instanceBlackrock DepthsBlackrock SpireMolten CoreBlackwing LairNaxxramas
My favorite instance is Gundrak.
Favorite instance? That's a hard one; I'm a big fan of Ulduar and basically anything Northrend. :3
I like Grimrail Depot. The concept of being on a moving train (even though it doesnt really move) is awesome. I just wish the camera positions were better.
Stormstout Brewery... beer rules :)
The Scarlet Monastery, so much history. You can get a glimpse of what Warcraft was like.