I thought with the collective gaming experience we've all got, it would be interesting to see what everyone's favourite or best 'level' in a game is. This could be anything from the most awesome designed or artistically pleasing virtual environment you've been in. I know there is awards given out for level design, but I just wondered what everyone else thought.
Two which stick out in my memory are the Mansion level from Vampire: Bloodlines which you have investigating the place because its suspected to be haunted. Even though the path was fairly linear, I thought the use of 'ghosts' was cool and has to be one of the scariest levels I've played.
The other is the second island you visit in Riven, I thought the whole thing was utterly captivating as every aspect of life their had been carefully thought out. Even with very little written content you could visually piece together how the people who lived their went about their day-to-day business.
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Here is a roughly compiled list of the levels we've been talking about. I composed it by counting the times people have positivity spoken about the environments. Its by no means accurate, but it gives a good idea which games to buy if you want to be impressed by the level design.
The GOG list of best levels we've played:
1) Thief Deadly Shadows: Shalebridge - 9 Votes
2) Half Life 2: Ravenholm - 8 Votes
3) Psychonauts: Milkman - 6 Votes
4) Vampire Bloodlines: Haunted Hotel - 5 Votes
5) Psychonauts: Lungfishopolis, Hitman 2: Opera, Half Life 2: Nova Prospekt - 4 Votes
6) Fallout 3: Tranquillity Lane, Half Life 1: Surface Tension, Doom: Level 1 and 2 - 3 Votes
There has been many others!
Including: Half Life 2: Citadel, Hitman: Hotel, Freespace 2: Massive Ship, Bioshock: Intro level, Thief: Bafford's Manor, Metal Gear Solid 4: Shadow Moses, Fallout 2: Navarro Base, Myst 3: Amateria, Unreal: Vortex Rikers, Splinter Cell Chaos Theory: Museum and Unreal: Nyleve's Falls.
Games on GOG to purchase
Freespace 2
Fallout 2
Unreal
Hopefully we'll see more of these titles popping up!

my favorite would have to be the Citadel section in Half-Life 2. It was very different from what you were doing in the rest of the game, and riding in those little pods was awesome. As you reach the top, I love how there's this one gigantic window showing how far up you are before ending and leaving you back in that cold, dark tower...
Oh, and I loved Riven, too. Especially that one tram that went underwater. Passing through those glowy rings at that speed was such a surreal experience.

The best bit of Half Life 2 for me was the bridge, I thought that was very well done, a real sense of scale.
The final level of the shareware episode of Doom, the two demons and the vast pentagram (pentacle?).
A lot to choose from the Ultima Underworld games, but Talorus Keep sticks in the mind.
Most of the earlier missions in the Hitman games were wonderfully fun. There was one with a hotel... can't remember which one now.
Many of my favourite games don't have levels...

Shalebridge Cradle from Thief: Deadly Shadows.

One thing that sticks out for me is just a visual in NWN2 (yeah, I know what most people think of NWN2). I was in an area where you're going up a mountain to face off with some fire giants and I just happened to arrive near the top at dusk, game time. I turned to look across the valley as the sun was setting and the sky was changing color. My jaw dropped and I sat there for a couple minutes just enjoying the view. It was gorgeous.

C'mon you bring up Half-life and didn't mention Ravenholm? For a quite a while after I finished HL2, I couldn't bring myself to revisit Ravenholm. Part of the unease came from Alyx foreshadowing the horrors that went on in Ravenholm. Just seeing the way her face reacted to the memories of what happened there was enough to instill this sense of dread in me when that sealing door shut behind me.

The 'Hell' level in Painkiller.

Lungfishopolis - Psychonauts (Goggalor FTW)

The 50's virtual reality suburbia in Fallout 3. Just very very cool.
Not sure it's my fav, but I can't think of many.
Ooo, oo - the end of Freespace, battling that MAHOOSIVE frigate/whatever in the wormhole. Bitchin :D.

Ah yeah, good call. The whole intro level to Bioshock was fantastic.

Definitely agree on the 50s VR level in fallout 3
The worm innards in Gears Of War 2 was nice & different
The opera level in Hitman Blood Money was brilliant, pulling the old switcheroo with the prop pistol...
The Tzmisce snuff movie house in VTM Bloodlines was really cool as was the haunted ocean view hotel. And playing as a malkavian... ahh that game just rocked

Escaping Zebes in Super Metroid was pretty cool.

Bafford's Manor in the original Thief. Everything was perfect in that level. From the guards conversation about how they don't make bears like they used to, to the actual layout of the manor. There were so many little secrets in there and just the atmosphere that the place gave off was just unreal. I have yet to experience any level in the newer games that have so much win in them like that first Thief level.

Shalebridge cradle from Thief 3 as Vagabond said...very atmospheric.
We won't go to Ravenholm and Nova Prospekt chapters from Half-Life 2. The daylight part of Pegasus mission and the first part of Red square mission in Call of Duty 1. Yes, it is just a stupid arcade (at least for me), but it was great anyways.