Underworld BGM - The Legend of Zelda (NES)
The Underworld BGM tune plays in underworlds 1-8 in The Legend of Zelda (NES). It has a nice lower, mysterious sound to it that keeps a feeling of dread in the underworlds.
The title comes from Famicom 20th Anniversary - Original Sound Tracks, Vol.1 album. The song is track 4 in the NSF file.
The song plays at 90 BPM and is in the key of G minor. It also uses the triangle channel as its lead instrument, which was usually used for bass.
Koji Kondo used a trick to make a reverb effect; by every second note played by the second square wave channel, the notes are able to overlap each other.