Tomb Raider: Anniversary/St. Francis' Folly

You enter St. Francis' Folly, get attacked by two jaguars, and get to watch a cutscene.

Main hall
You first need to get through the main hall, and the only exit is closed. While you can stand on the pressure plate in the middle of the room to open a door, it closes the moment you step off. There is a globe you can use to hold it down.

Climb the farthest two pillars, and jump to the ledges on the left-hand side. Make the appropriate jumps until you are above the entrance. This leads to a mural, which is reset by standing on the pressure plate ahead of it, and has buttons that can be lit. For the first combination, head to the right, and look at the door - note the position of the gems on the knife and eye. Shoot the two buttons to open this door.

The doorway leads to another formation of buttons on the right. Use this combination to unlock the gate blocking access to the globe. Pull the rings from the globe using the grappling hook, and push it to the button in the middle of the floor. The route above the door opens, and you use the pillars to get through the gate. When you climb down and open the main doors, you are attacked by two more jaguars. After the combat, you can move the globe to the second button.

After going through the corridor, you will enter a large vertical chamber.

Poseidon
Inside the Poseidon gate, you will first encounter a portcullis. To get past it, pull the lever on the right, and grab the bar on the portcullis. Jump to the left, wait for it to drop, and jump backwards to catch the middle ledge (and climb through).

Enter the water, pull the lever, and enter Poseidon's vertical shaft.