In the next room there is a red-and-gold structure with a swinging blade in the middle and a break-away tile (51/51) below the blade. Walk down the slope and stand facing the blade and cracked tile. To avoid taking damage from the blade, try to line Lara up with one side of the cracked tile rather than the middle.
Hop back, then take two more walking steps back. Wait for the blade to swing toward the side of the tile Lara is facing. (This will ensure it's moving away from you when you reach it.)
Then take a running jump and continue to hold Jump and Forward.
Lara will land on the edge of the break-away tile then take a running jump into the opening beyond.
- OR -
Alternatively, walk to the edge and take a standing jump to grab the edge of the break-away tile.
It won't start to crack until Lara stands on it, so there's no rush. When you're ready, pull up...
...and immediately take a running jump past the blade into the opening.)
This is SECRET #3. Inside you'll find a large medi pack and 2 sets of Uzi clips (18-20).
If you've found all secrets in Atlantis, you'll unlock the "Codex of Atlantis" achievement/trophy here. And if you managed to shatter all of the break-away-tiles in the game, you'll get "After Us the Deluge" as well.
Return to the doorway, walk to the edge, and look down. That eensy-weensy square opening filled with water is where we're headed.
Stand in the middle of the doorway, take one walking step back from the edge.
Then swan dive (Walk + Jump + Forward)...
...into the tiny pool below. This trick unlocks the "Bullseye!" achievement/trophy. Look at you go!
Pick up the Uzi ammo (21) on the bottom of the pool.
Then follow the underwater passage until you can surface.
Climb out of the water and pick up 4 more sets of Uzi clips (22-25)—and the final save crystal if you're playing NG+.
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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