Return to the pool below the COMPUTER ROOM and pick up 2 bundles of harpoons: one is behind the rock formation just to the right of the rusty metal opening leasing back to the entrance. You can reach the harpoons by swimming to the top of the rusty metal structure, then down to the right; or by swimming around the right side of the rocks.

Here Lara has approached the harpoons from the right.

The second bunch of harpoons is on the opposite side of the cavern, directly below the enclosed walkway, amid the sparkling mutagen on the sea floor.

Swim up the white funnel to get air at the trapdoor between pickups if necessary.

Now go for the secret. Swim across the cavern toward the enclosed walkway. Swim down between the leftmost support pillar and the one next to it. Here you'll find a narrow tunnel in the rock wall.

Swim inside to get the attention of another mutant fish.

Roll and swim back out of the tunnel...

..and into the open cavern. Then roll again...

...and harpoon the fish as it approaches.

Or, lead the fish back across the cavern to the yellow opening and shoot it from the ledge (as shown in the previous section).

After you've dealt with the fish, swim up the white funnel to the trapdoor for air.

Then return to the tunnel and follow it a small room with a window looking into the RESEARCH LAB.

Pick up the grenades and loaded GRENADE LAUNCHER. The weapon is SECRET #3.

Turn around, grab the large medi pack, and head back through the tunnel the way you came. Return to the white funnel for air before going on.

[Return to the Sleeping with the Fishes Walkthrough]