Final Fantasy V/Fire Lithograph

Submarine
The ariship hangar is visible again so dock there. Enter and go down two levels to find Cid trapped in some machinery. You rescue him and he and Mid start to work installing some new technology in your airship. When it's nearly done, Mid find Krile waiting on deck and they talk about Cid blaming himself for the loss of the crystals. Cid appears and announces that the work is done. In saying farewell, Cid says that, seeing as he can't fight himself, he's glad he could help the effort with his inventions.

When the airship is on the ocean surface, press the confirm button and then select up or down to either take off or go under water. There are four points of interest marked on the undersea world map. One is a shortcut to Moore Village, so there is nothing new there. Two others lead to the remaining two lithographs and the final one leads to the, now sunken, Walz Tower. Apparently, these can be explored in any order, so we'll start with the one leading to the Fire lithograph.

Great Sea Trench
Pilot the airship to the eastern edge of the worldmap, submerge, and head for the point marked northeast of Crescent. There is a crack in the ocean floor there; when you're above it the sub docks itself. Exit the sub to an undersea cavern. Defeat the Gargoyles as with with previous lithographs. A page from the book burns and the door is opened as before. Go in to B. 2 Floor. The monsters here are undead and there is lava around, so it's a good idea to have a Geomancer and a Bard in your party.

Follow the passage east, then south and down the stair to B. 3 Floor which has a save point.