Note the vegetation-covered ledge jutting out of the wall on the left side of the room. The greenery conceals an opening, but the ledge is too high to reach from the floor.
So climb up on either side—to the landing with the pillars on the left or the stone ledge on the right—and take a running jump to the ledge with the greenery.
Inside is SECRET #3, a large medi pack (5) sitting on the floor to the right.
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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