After using the SUN TALISMAN, as described in the main walkthrough, the doors near the SMALL POOL WITH TWO OBELISKS will be open. If you want all the secrets, go through the SOUTH DOOR before the one to the west.

It leads to a tall room with a vertical pole and a pool below. Run off the edge...

...to land in the deeper part of the pool.

Swim down to the right to get some shotgun shells. Then roll, return to the surface...

...climb out on the right, and pick up the Uzi clips sitting on the bottom.

Move around to the other side of the pole and dive down to get some wideshot shotgun ammo. Swim into the flooded passageway...

...and pick up a small medipack in the alcove on the right. Position Lara facing the gray tile in the middle of the square door and press Action to open it.

Return to the surface for air if necessary. Then swim through the door you just opened and on through the diagonal opening ahead. (As in the other underwater area, if you stick to the upper/left side of the diagonal opening, Lara is less likely to get stuck.)

Follow the passage forward then right, through another narrow opening.

Continue onward and upward to a small room with air and a SECRET (30/70).

Here you'll find three pedestals displaying wideshot shells, a large medipack, and a new type of crossbow ammo: explosive arrows. (Still no crossbow, but keep collecting those arrows!)

Return through the flooded passage the way you came. Surface, and climb up to the vertical pole.

Stand close to the pole and hold Action to grab onto it. Climb up until Lara is hanging just above the greenish horizontal stripe on the wall. Pivot so the small ledge with the flares is behind her.

Then press Jump to backflip onto the ledge. Pick up the flares.

Then jump from the corner of the ledge to the doorway. Follow the corridor back to the POOL WITH THE TWO OBELISKS

[Sacred Lake Walkthrough]