The Hidden Blade Assassin's Creed in Depth

Can you guess how this video will end from reading the title? The interesting part starts at 3:40.

AC2 stops modeling certain things if you go far enough away and come back. That includes the closed door to Maria's tower and even Maria herself! You have to go very far away to make Maria vanish.

The first time at the top of the tower, don't step into the light or else it will trigger the cutscene. Go around the edge and do the leap of faith.

Now run all the way back to where Altaïr started the dream sequence and climb over the building that was behind him (to the northeast but you don't have a map during this part of the game). There's a memory wall just before you reach the Cathedral of the Holy Cross. I actually break through the memory wall for a moment. Don't go too far or stay too long else it's instant desynchronization.

When you come back to the tower, the door is standing open and Altaïr can at last enter. Unfortunately it's just an empty triangular room with a low ceiling. There's no staircase as implied by Maria's actions.

The fun really picks up at the top of the tower. Maria has vanished. Only her hood remains, which falls to the ground because she's not there to support it. I suspect the game developers used a cloth simulation engine to make her hood drape realistically as she pulls it back from her face. The rest of her clothing is part of the character model and is also invisible.

The game sort of freezes up on the final camera angle of the empty hay. You can still move Altaïr around a bit and see his shadow move. I tried to do the leap of faith and somehow landed with a thud, shaking the camera for a moment.

Thanks to Jami-bunny for finding this glitch and sharing it with me.