From the start go all the way down the path until you reach the first door on the left which is a Secret Room. Then, get to the floor with tiles that look like brightly colored flowers. Go left here. Go down the stairs and through the door. In the next room just jump down to the bottom, there will be some gbusmsira in here, after they are dealt with, go into the next room. You will see a Blue Device sitting on top of a central pillar. Jump up and hit it enough times so that it spins the room and makes a new exit. Jump up and go through the window like structure, follow the path until you get to an orb dispenser, hit it to generate orbs. Keep following the path, once you go a little ways down the hill, a ball will start chasing you, you might want to equip the quick heart for this area (or just evade a couple of times), because if you get touched by the ball you'll have to fight some enemies. In the next area, you'll see a big gigantic meat tenderizer or something like that. Wait for it to rise to the ceiling, then go destroy the door, if you don't destroy it on the first go, then run back and wait for the ceiling to rise again. Turn around and you'll see a door has opened in the wall where you first entered. Jump behind you up the wall and follow the path up to an alter where you will find a sword Merciless. After retrieving the sword climb the wall and jump on top of the alters roof and collect the fragment of the blue orb. Return to the meat tenderizer and follow the path and go up the steps. In here, leap up to the platform on one side of the wall, then leap up to the next platform, once at the end of this platform you should see some floating pink tiles, jump on them. From here, jump onto the next set of pink tiles, then jump onto the purple ones, but beware, they vanish occasionally. After the purple, land on the pink, then from the pink land on the solid platform.
Now from this platform you should see two purple tiles hovering above you, jump up onto them, then go through the doorway and follow the hall to the end, the submachine guns are stored here. Run back the way you came and land on the platform below the purple tiles, jump from that platform to the next one until you see two more purple tiles hovering. Jump from those tiles over to the next platform, then jump to the next one that has the blue crystal on it. Hit the blue device so it activates. Now jump down to the bottom and walk onto the red tile, it will rise all the way to the ceiling, jump off to the platform and go through the door.
Follow the path until you come to three statues, you will have to break all of them to get the heart in the next room, weaken all of them so they have 1-2 hits left, then just break them all and use the quick heart plus Devil Trigger to reach the heart before they regenerate. Now go down the hole in the room with the heart and you'll get a cut scene of the next boss, Bolverk....
Bolverk is accompanied with Freki and Geri. Go for Bolverk first but you can always get rid of the annoying Freki and Geri if you want to. Generally, just dodge his slashes and plink at him from a distance with your guns. When you get close to him and he disintegrates into a blue cloud, he will come down from above with a surprise attack, you also must watch out for when he decides to use the Stinger on you. Bust some caps in him and Freki and Geri and move on the next mission.