The following secret doorways can be found if all the sentinels are already defeated before killing Thane again. All these rooms will link into a path way to the veranda (the pathway to the doorway to the MX-Goliath and the top of the tower to Thane):
Combat Arena After taking down the large creature (the one with no weapons and attacks with claws and teeth), notice that a tree has been growing in the arena. If you are going after the Stone Demon first, the tree will not be there, however if you are going to Thane for the second time, the tree will be massive. This gives you the option to climb the tree if you do not want to go down the area where the Stone Demon lies. The tree will take you to the veranda near the top of the tower (before the doorway of either Thane or MX-Goliath).
Archivist Area Once the Archivist is defeated, a pathway will become available. This will take you to the room where you must defeat a guard. This room also has six locked doors with a weapon imprint. If you have the weapon with the matching imprint, you can unlock the door and claim whatever is inside. Proceed to the next room, where you enter a hallway near the veranda.
Stone Demon Shrine Cavern Once the Stone Demon is defeated, a pathway on the other side of the bridge will become available. On this pathway you will have you battle another large creature (similar to the one in the combat arena). Defeat him and use the stairs that lead you up the side of the tower to go to the veranda (before the doorway of either Thane or MX-Goliath).
MX-Goliath Room The right side of the room with have a pathway that leads to the top of the tower.
Defeat the following opponents to unlock the corresponding items:
Up to four cash bags (two usually left of the rock writing and two usually near the shrine behind Siris), small key (left of rock writing or during intermission sequence when Siris and Archivist are talking when the camera falls behind the wall; there is a very close small key there).
Five or six cash bags, sometimes one full health, and one large chest at far left of the room.
Four cash bags (one behind shrine, one under bridge, one on the bridge close to shrine, one on ledge before the bridge), usually extra three cash bags in the small temple where Siris enters the room, and large treasure chest before the bridge.
Up to eight cash bags, one full health (on the stone ledges), one treasure chest (open after second kill), and medium key (behind chair left of Thane's chair).
This glitch gives you plenty of money by selling unlimited Infinity Blades you can get for free. First, complete the game at least once and have mastered the Infinity Blade. Right after completing the game and starting again, go through the whole tutorial until you are up to a long cut scene. You will verse the 1st major boss. After you defeat her go to your inventory, switch from the Infinity Blade to any other weapon in your inventory. Sell the Infinity Blade and exit the inventory, then continue to the cut scene Right before Siris puts the Infinity Blade in the rock, go to the inventory and you will see that you have the Infinity Blade again. After the cutscene ends there should be another cut scene. Right when it starts, go to options and go to restart rebirth 1. It should start from the beginning of the tutorial. At the start of the tutorial the 2nd time if you used the right items (Nodus, Eridius, Seratic Armor, and Ring of Ice and Fire) you sould have 2 of all of them, sell them . If you did everything correctly you should have earned $381,068 each time you do this. Repeat as many times as desired.