You need to hit the door with something you can find on a shelf in the east. There are two skull faces on walls. They look like twins. You have to hit the skulls in the right order. Save first before you hit them so you can redo. They remove a column. If you remove the column, you can get to the item you need to equip to hit the door. To remove the guy who is blocking your way, you have to find a sphere and tap it. You'll need to hit many crackable walls to reach the sphere. These maps should help. The crackable walls are in the southeast and show up in the second pic as walls with little dots on them.