In Rune Factory 2 near the end of the game, after you've collected all the tablet fragments, Barrett will mention something being sealed under the city. He'll also say that theres no way to get under the city. This isn't true, to get under the city you need expand your barn until it's at the 28th floor. Once you have that final floor built there will be a hole in the floor. Going through the hole takes you to dungeon under the town. You need to be ready to fight because the monsters there are extremely strong.
Added by: Ninetailed Fox Mar 6th 2011, ID#15340