After collecting three pendants and facing the evil wizard Aganhim, Link is thrust into a mirror version of Hyrule. Instead of lively forests and friendly villagers, this Hyrule is speckled with dust, dried up trees and inhuman natives. Upon entering, you're treated to the best piece of music from LttP - the Dark World theme. It's equal parts unsettling and exciting, and subtly suggests that even though Link has been through so much already, there is still a long road ahead.
The lead tune, coupled with a constant set of marching drums and brass, gives Dark World a haunting persistence reminiscent of a villain slowly transforming a bountiful world into wasteland. And that's exactly what's going on in the game, so this track fits the bill.
Official soundtrack
You could try to find the aforementioned "Sound & Drama" CD, but in the interest of providing another option, try to sniff out Zelda: The Music. Good price for 70 songs spanning seven games.
Remixes of note
Remixer Beej has constructed the deliciously noisy Fragments of Gold, a thumping dance track that'd feel at home in any club.
If you're more up for a slow, poignant trip through the game's ending scene, McVaffe's Darkness and Light makes the tune a little more touching.
Long Dao's recent Lost Dark World tries to mix the original's sense of fright with a Jurassic Park-esque level of grandeur. It works, but six and a half minutes is four too many.
Zelda II consistently gets a bad rap for being the series outcast. Say what you will of its side-scrolling, magic-using, level-gaining ways, the music from Adventure of Link was far superior to the original in terms of complexity. And nowhere is that layered, deep growth more apparent than the Temple Theme. It's not necessarily invocative of anything, it's just fast, crazy and loaded with catchy riffs. Unlike the original Zelda's tracks, this one keeps building, making the final cut over three minutes long with one loop.
Nintendo knows how great this song is; it appears in both Melee and Brawl as one of fans' favorite ass-kicking anthems. This song's so effing hard you could set it to a bad ass car chase and it'd still work.
Official soundtrack
As with any game soundtrack, especially those from the NES, finding sound files is easy. But if you like it so much you want to give more money to the cause, Famicom 20th Anniversary Original Sound Tracks Vol. 2 contains plenty of Zelda II songs.
Remixes of note
If you need to get people dancing, like now, bliNd's Temple Trance will get 'em up and moving in seconds. An aggressively mixed view of Zelda II's best track.
