Keep going deeper and deeper in that basement place. You must have not done everything there yet. You have to destroy a pillar so that it falls and it the pillar that is blocking the door in the treasure room is destroyed. If you need further help refer to the anyone stuck forum.
Lets live together, I don't know how long it will last, but it doesn't have to be for show, together, till death do us part. - Kenshin "Shinta" Himura - Rurouni Kenshin