Great thread Sc, here's some of my favorites:

Phendrana Drifts (Metroid Prime)



Hyrule Castle (The Legend of Zelda: The Wind Waker)



Casino Night Zone (Sonic the Hedgehog 2)



Skytown (Metroid Prime 3: Corruption)



Nippon (Okami)



But my favorite has to be Sky Sanctuary Zone (Sonic & Knuckles)



Gorgeous!

Content Bump:

The entire world 8 of NSMBWii has pulled itself into one of my favorites. Especially for how smart they used the environment with the gameplay necessary.

MapleStory - Time Temple.

Dracula's Castle - Castlevania: Symphony of the Night

Hyrule Field - Twilight Princess

Ganon's Castle - Ocarina of Time

and more

Megaman ZX Advent Final Stage part 2:

-Awesome music.

-Awesome idea

-Very hard.

I can't remember the exact names:
Super Mario Rpg: The forest were you meet geno
Chrono Trigget: The kingdom of zeal

I too will add Phendrana Drifts from Metroid Prime. Incredible combination of music and atmosphere.

Also the Buoy Base Galaxy in Super Mario Galaxy, the Forsaken Fortress in the Wind Waker, Prison Island from Sonic Adventure 2, and Hanenbow stage from Brawl.

Hmmm... Probably the baths from Sands of Time, Egyp/Future zones in Crash Bandicoot 3, Hades in the God of War games, Racoon City in RE3, the Village in RE4, space arena maps in Quake 3, island of Gust in Phantom Hourglass, the cathedral in Tekken 5 and pretty much all levels from Rayman 2