After climbing into the left doorway on the north wall of the ROOM WITH LEDGES AND SWINGING BLADE...
...follow the passageway to a gap above the mossy room where you found secret #1. Turn around and drop back to grab the edge of the floor. Traverse to the right until you can pull up.
Follow the short passageway to a switch. (On the way, you may hear the secret door in the room below closing.) Use the switch to flood the room below.
Drop down into the water and surface right there. Don't bother exploring underwater. You already covered that area when you went after the secret. Instead, swim along the surface to the doorway just above water level.
Climb out and kill a rat (4). Go to the end of this short hallway and jump into the water again. Follow the twisting passageway...
...until you can climb out of the water in a room with spikes on the floor. Stay on the step at water level until you've killed the lion (5) lurking here.
In the U-shaped passageway opposite the spikes, there's a switch. Use it to open a door above. Return to the spike room and climb into the alcove opposite the spikes.
From here, you should be able to kill the 2 gorillas (6-7) in the room above using pistols. (There's also a save crystal here in NG+.) When they're dead, take a standing jump to grab the floor above and pull up.
Move to the edge of the hole above the spikes. Take a standing jump to grab the crevice to the left of the doorway and traverse right until you can pull up. Enter the room and pick up a large medi pack (8) and a GOLD KEY (9).
Jump from the doorway over the hole with the spikes below to land on the safe floor.
Return to the edge of the other opening in the floor and take a standing jump with Action to land in the alcove below. Proceed forward into a long, narrow room with a pool. Use your GOLD KEY in the keyhole here...
...to raise a series of floating blocks in the pool. Make your way across the blocks using 3 running jumps then a standing jump. (With tank controls, you'll need to set up each jump, since the spacing between the blocks doesn't allow for a smooth series of running jumps. If you slip, return to the start and try again.) Pick up the small medi pack (10) to the right of the door before going in.
DARK MODE: Even with brightness adjusted, dark images on a light background can be hard to see. May I suggest a reputable dark mode browser extension, such as Dark Reader? (Download only from trusted sites, like darkreader.org or your browser's web store.)
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