Band Land

That thing he's riding on? It's a maraca.

Some video games contain surreal, whimsical settings for no particular reason. Apparently, one such setting type is far more common than you might expect. Quite a few video games have levels or other areas that are music-themed. No, we're not talking about an Unexpected Gameplay Change to a Rhythm Game here. (There might be a music-themed Mini Game or three, but that's not the whole point of the place.)

These levels make you "face the music" in a more literal fashion. They're made of musical instruments, sheet music, or (somehow) music itself, often of giant scale. You might get blasted out of a huge trumpet, walk gingerly along a giant keyboard, or slide down a musical score. Often, moving around and interacting with your surroundings will "play" at least a few of the instruments. If the level designer is feeling especially playful, the background music itself may even be affected by what you do in the level. As these settings tend to be light and comical, they're sometimes used to indicate a Breather Level. But don't count on it.

Compare Disco Tech.

Examples of Band Land include:

Film

Yellow Submarine: Pepperland.

Video Games

Aero the Acro Bat 2 had Disco Fever.
The music levels of Bubsy II
The Trope Namer is Band Land from Rayman.
- Rayman Origins resurrects it as the Desert of Didgeridoos, which combines Band Land with a side-order of Shifting Sand Land and a little bit of Gusty Glade.
Planet Sonata in Ristar, which, as its name suggests, is made out of musical instruments and more abstract representations of music. The first stage of the planet even has you rebuilding the background music, bar by bar.
Stardust Speedway in Sonic CD, which looks like a giant brass instrument.
- Music Plant in Sonic Advance 2.
Musical Town, the sixth level of Sparkster (SNES).
Squidward's Dream in SpongeBob SquarePants Battle For Bikini Bottom. In no way a breather level.
Super Monkey Ball. Advanced Floor 11 is about rolling your ball on the strings of a giant guitar. It's definitely not a Breather Level.
- Advanced Floor 18 is a downhill ramp in the shape of a treble clef, where you start in the middle of the spiral part and have to chase down the goals, which have a small head start and ski down the ramp.
How about an entire game made of this trope? The obscure Sega 32X game Tempo comes about as close as one can get to that: although the levels are quite varied, they all have some sort of musical motif.
Another whole Band Land game: Brutal Legend.
An area of Toontown Online, "Minnie's Melodyland", features whimsical musical-themed fun.
Slightly-obscure platformer Vexx has a sub-level inside one of the worlds composed of nothing but floating musical instruments. You get there by jumping inside a giant piano. No, it doesn't make any sense.
The first level of Wayne's World(SNES), set in a music shop full of various homicidal instruments.
The second level of World of Illusion (mostly a sky-plus-mountaintops level) has segments that take place on giant keyboards suspended in space where stepping on each key generates a musical note that randomly changes into an item or a bomb.
The second level of Zool has a general music theme, with not only musical instruments but also stereo equipment.
This is probably the best term for where Eternal Sonata is set, though a lot of it's a matter of Theme Naming.
The 'Sixties' theme in the Rollercoaster Tycoon 2 expansion Time Twister includes lots of parts for building this kind of theme park.
In Megaman Battle Network 3, Mayl's home page has a background with part of a detailed musical piece.
The first level of Parasol Stars features instruments as enemies, with a matching boss.
In Super Mario Galaxy 2, a section of the Cloudy Court Galaxy has drums and a cymbal that you can jump on.
- Mario Party DS has Toadette's Music Room, which is...yeah.
Melody Town in Kirbys Epic Yarn.
In Purple, you will occasionally have to pass through colorful corridors inhabited by flying deadly instruments, while clavinet music plays.
Mario Kart 7 has Music Park (or known in Europe as Melody Motorway), which sees you driving past giant trumpets, across piano keys and jumping over tambourines.

Web Comics

The Land of Quartz and Melody in Homestuck, which is themed around music boxes. The Land of Heat and Clockwork also contains a few hints of turntables, such as the Beat Mesa.

Western Animation

In the 1980's special Puff the Magic Dragon and the Incredible Mr. Nobody, Puff and a boy named Terry travel through the Fantaverse, which includes Cleftomania, a land made of musical instruments. They are instructed to "proceed harmonious through," but have to tame the Savage Beast first.
One of Disney's "Silly Symphony" shorts portrayed rival nations called The Land of Symphony and the Isle of Jazz, inhabited by anthropomorphic musical instruments.