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.