After using the undead knights to break the barrier and climbing up into the next room, as shown in the previous section, follow the passageway...

...to cavernous room with reddish stone walls and torches burning in wall sconces.

Pick up Uzi ammo just inside on the right and flares in the alcove to the north of the ammo.

Once you have the flares, drop down off the ledge and cross the big room to the west side.

Here you'll find a deep hole near the wall. Move around to the left side of the hole.

Drop and hang from the edge, let go, and quickly press Action again to grab the edge of the opening.

Crawl inside and follow the tunnel to the end.

Drop down into the passageway below.

Turn around, jump up the steep part of the slope, and continue to the top.

Pull up onto the ledge directly ahead. This is SECRET #2 (62/70).

There are several items in the room above, guarded by another pair of undead knights. If you pull up on the right side of the opening...

...you can step forward and grab the first pick-up: some flash grenades.

Then side flip to the right to (hopefully) avoid the knights.

Grab the revolver ammo, flip or sidestep to the right, and take the large medipack.

Now flip back to the left twice to avoid the knights. Lara should land next to the wall near the opening where you pulled up.

Roll and sidestep twice to the left. (She'll move to the right since the camera is now facing her, but you'll want to use the Left control.)

Then jump forward across the hole in the floor.

Pick up the explosive arrows, turn right, run forward, and grab the wideshot shells.

Then run forward and slide down the ramp to safety. Don't worry if Lara takes a little damage. The end of the level is near, and her health will be restored.

[Citadel Walkthrough]