When in the cellar of the pentagram room, there is a lever on the table which you can click to move the statue above to reveal a stairway. The next room has the 3 keys and crystal bag.
The level 2 BF key (which opens the second dungeon) is not too far from where you are now; it is possible to find it shortly after getting into the citadel. The level 3 key is available near the end of the act.
