The Sealed Cave (封印の洞窟, Fuuin no Doukutsu?) is a dungeon in Final Fantasy Adventure.
Sumo finds the cave's entrance within the Palmy Desert sands and ventures inside looking for the ultimate magic of Nuke which was sealed by Lich.
Lich is eventually defeated, and Sumo learn the Nuke spell. He then heads back to Ish.
Spoilers end here.