So, I'm asking you this: what do you think are the most memorable video game levels / missions / tracks of all time?
Here's my personal top 5:
1. World 1-1 from Super Mario Bros.
http://themongomania.files.wordpress.com/2008/06/super-mario-bros-duck-hunt-u-_001.jpg
Is there anything left to say about the good ol' 1-1? Almost every gamer knows this level by heart.
2. Hollywood Holocaust from Duke Nukem 3D
http://www.happypenguin.org/images/2003_04_03_150737_shot.jpg
To me, this was the first time I ever played an FPS game. This place had so many secrets, so much things to smash, so many aliens to shoot... Good times.
3. Ravenholm from Half Life 2
http://cerling.files.wordpress.com/2010/01/ravenholm.jpg
Dark and unsettling... Very little ammo... Respawning zombies... Yikes!
4. Green Hill Zone from Sonic The Hedgehog
http://www.freshlabs.de/journal/wp-content/pics/sonic-greenhillzone.png
Memorable in the same way as World 1-1. Again, not much left to say about this one.
5. High Speed Ring from Gran Turismo series
http://nand-magazine.net/images/gt-psx.jpg
Gran Turismo was one of the first driving games I ever saw and High Speed Ring was the first track I raced on. It has been in every GT game since the first one!
Now it's your turn! Tell about the great or otherwise memorable levels you have played.

I swear we've had this thread before, but never hurts to give it another go...
Freespace 2: Dive
http://www.youtube.com/watch?v=UrchciHCI8A
Thief 4: Shalebridge Cradle
http://www.youtube.com/watch?v=CkuKpAu0G3o

Doom 1 - E2M8
Chronicles of Riddick - Fighting match at underground mines
Deus Ex - Hong Kong
System Shock 2 - Engineering deck
Planescape Torment - the Hag's abode

1. The final mission of Doom episode 1 (Knee deep in the dead).
Just walking down that corridor, before hearing the walls move. At first I didn't realise what the shape was... (too busy trying to kill the two cyberdemons!).
2. Baldur's Gate II: Shadows of Amn (okay technically not a level)
You're in the sphere, and you need a demons heart. You stop to get one, and this doesn't need to take long. I uncovered all the fog though (bit of a completionist) and looked at the map...
3. Flashback
The "running man" level... always liked that one.

Oh and Wolfenstein 3D - last level of Die Fuhrer Die.

Halflife: Xen...
For all the wrong reasons -_-

Super Mario World: Giant land Fuck The World!!

The Secret of Monkey Island:
- ... Monkey Island of course :)
Contra:
- The Jungle
Max Payne:
- Final stage (skyscraper)

Seconded. It was really fun.

The Citadel section in Half-Life 2, the level that's pretty much The Rock backwards in MW2, the part when you have to take pictures for that freaky dude in BioShock, the ship level in the first Modern Warfare, Doom E1M1, that level where you shoot at people on a boat in Time Crisis 2, the train level in Splinter Cell: Pandora Tomorrow (GOD THAT TRAIN LEVEL WAS SO AWESOME), that cruise ship level in Splinter Cell: Double Agent, and so on. Those were just off the top of my head, I'll say more when I think of more.

Fort Frolic - Bioshock.
The Milkman Prophecy - Psychonauts
Dark Carnival - Left 4 Dead 2
The Hotel (Forgot the name, think it was something like Oceanview) - Vampire: Bloodlines
All I can think of right now.

Chapter 10 of Dead Space was pretty memorable, the crew quarters stocked with corpses and foreboding, then things go quiet and you hear that deranged woman (who you never find) singing twinkle twinkle little star

Hell - Painkiller.
Beast Island - Doom 2: Alien Vendetta (custom campaign).
Black Velvetopia - Psychonauts.
The brothel - Planescape: Torment.
The mansion - Max Payne 2.
Chapter 4 - The Witcher.
The titular level - Braid.
Templar Cathedral - Deus Ex.
Scrabania - Oddworld: Abe's Oddysee.

stargate on genesis-whole game was epic... http://i.ytimg.com/vi/zvhR0qvIZcg/0.jpg

- dead rising: the children section, with the big roller-coaster
- the hotel level in vampire the masquerade bloodlines
- the netherese ruins in neverwinter nights (shadows of undrentide)
- the beginning of prey