Go back to the previous area now and grab the cart and push it up against the house in the open area. Head to the door and lift the wood blocking it and open it. Walk up the stairs and jump over the wall in front of you and you'll be on the other side of the door you were just in front of. Move it under the broken ledge and jump up onto the cart, then jump up onto the ledge. Walk up to the front of the cart, the part with the two poles sticking out and grab the left one with your left arm and the right one with your right arm as this makes it easy to maneuver it. Now that you're across the gap and have breached the castle walls, you'll notice a cart in front of you and a broken ledge as well. Launch yourself with the catapult in 'Castle' Once you're in, grab the brown lever to your right and push up and you'll be launched into the air, unlocking:

Once the wall is broken, turn the wheel again to bring the sling down and climb in. If it doesn't, pull or push the catapult to change the distance. This will launch a rock and hopefully break the wall across the gap. Pull the catapult back a bit, then put a rock into the sling and grab the brown lever just to the right of it and push it up. Head over to the left side of the catapult and turn the wheel over here clockwise to lower the sling. Open the door and head to the left and you'll see a catapult.

Once here, jump to the platform with the door, open it, and continue outside. In this next room, head up the stairs to your right and once you're at the top, jump up to the window ledge and pull yourself up onto it.

Once it's out, pull the door open and continue on.

Once it's broken off, grab the lock handle from either side and wiggle it out of the door. Now at the start of the level, pick up the rock close to you and swing it against the lock until it breaks.

Human fall flat castle level