Tower of Hera (A Link to the Past)

The Tower of Hera was the third (or fourth, depending on if you count Hyrule Castle as a dungeon) in A Link to the Past. It wasn't too challenging, but it was harder than the previous two dungeons. Link found the Moon Pearl inside the tower. The boss was Moldorm.

Note: In the GBA remake, this dungeon was renamed, "Mountain Tower".