Problems you can't kill

Floors, arch enemy

Even though you defeated the vampire everything is still going wrong with the Earth crystal and the surrounding lands. The problem is even though you are four awesome warriors and magicians, all of your power is useless against a beefed up floor tile. Even worse unlike the problems with the elf prince there is less of a trail of breadcrumbs for you to follow.

No attack on this titan

The solution is to leave the Earth cave and go to a cave in the west. When you go there, there is a titan blocking your path. However you have the star ruby that you find in the vampire's room, you can give the titan the ruby and he will wander off, satisfied with his new snack. Once the path is clear you can loot the treasure at the bottom of the cave as well as reach the stairs on the other side.

So there was more?

On the other side you can go to the other cave where there is a sage who just gives you a magic staff which allows you to destroy the floor plate. At least you don't have to get a pick ax. You can now go all the way down to the bottom of the Earth cave.