Use ur starting gun to find secret rooms. If u shoot a wall and the bullet impact is orange circles (as if u shot a light) then there's a secret room behind it (use L2 R2 to access). Typically rooms w/nothing surrounding them have secret areas. Every floor has a secret area and a secret dungeon, but secret dungeons can not be accessed w/a blank. Shoot walls and see if the impact is orange circles, then if u want u can use another gun to reveal a crack. Then use a blank.