When you first begin, follow Von Croy. When you get out of the corridor, there are a couple of pits you'll need to jump over. If you get caught in the large pit, don't worry, you can climb up the vines on the walls. (There's also a hidden shortcut in the right corner--might as well take it). Von Croy is waiting for you below.

When you cross through the archway and onto the next platform, you'll be given a strange perspective. Go ahead and just run off the edge. Then sprint through the doorway in front of you (dive and roll if needed) before Von Croy closes it. If you didn't make it through the door, don't worry. See those vines to the left of the door? You can climb up them and over into the next room.

Climb up into the corridor and follow it through until you get to the large room. Drop down to the floor and run to the other side. There are some vines on this wall so you can climb up. In the next room, you'll need to get up on one of those platforms. Work your way up to the top platform in the left corner. Turn to face the opposite wall, you'll know you're in the right place when some music kicks in. You need to do a running jump and grab onto the ledge on the platform across from you. Von Croy is waiting for you ahead.

Run across the bridge. Von Croy won't be going anywhere until you activate the trigger that will open the door--it's on the right wall. Reach into the hole and the door opens.

Go through the door and take either the right or left path--doesn't matter which, they both lead to the treasure room.