Stone Tower Temple, LoZ:MM
Prime example of the perfect classic Mario Paint candidate. Notice how I remove the 16th notes and slow the song down? Yeah...
Anyways, about Majora's Mask, it's not my favorite Zelda (OoT's got you beat, boy), but I concede it is by far the highest quality one ever released. We have the single greatest town in Zelda history, actual npc interaction (and hell lot of it), the absolute pinnacle of Zelda dungeon design, and a difficulty that isn't piss easy, but pretty easy. The only flaw would be short main quest (lol 6 day run) and it unfortunately has to vie with OoT for most fun speedruns (lol, even I can beat the game in 4 hours) and it even has to fight "classic" status with LttP, but screw it all. We all know it's the best.