The Lifespring Grotto was originally the place where men and mermaids could live together in peace, according to the mermaid who resides by the entrance. It is located within a whirlpool off the coast of Mount Duergar, and can only be reached via boat. Bosses from Final Fantasy V appear here.
The Lifespring Grotto has 20 floors, and its 20th-floor bosses are the toughest in the game. Floor 5 involves a mini-quest that results in the party discovering and engaging Gilgamesh, who has been skulking around a mermaid community, in combat. Floor 10 holds the gaping Atomos, who knows the dreaded Wormhole attack.
The final floor offers a player a choice, much like the Earthgift Shrine and Hellfire Chasm. Either Shinryu or Omega can be fought at Floor 20, but not both during the same run through the Lifespring Grotto. Both are superbosses, so the player will have an extremely difficult fight no matter which entity they select. There is also the option of bypassing either boss and exiting the Lifespring Grotto through a teleporter (only possible at 5th and 10th floors).
Treasure lists are static on each floor, but what varies is the number of chests each floor has, and these are randomly sorted for each run.
There is only one map where ten treasure chests can appear. This map is a castle with narrow walkways of invisible tiles (the tiles will occasionally flicker so players can see where they are, then disappear again). The ten chests will always appear, regardless of which floor the map was found on.
If the player chooses to fight Shinryu, apart from getting Shinryu's treasure, there's a treasure chest on the right. If the player chooses Omega, there is no treasure chest at all.