Left, right, hard to tell.
If you're on the beam next to the opening where you got the key, face back where the other beam fell when you jumped on it. Jump across that space. It's long, but it's doable. Get to the middle beam, climb onto
the stub over the water, and jump on the high stub nearer the entrance. Look at the wall over the entrance. Use the hand-hold ledge. You'll have to cross the room, drop near the water, whip back across the room, jump along the wall, cross the room again, jump and climb up, and figure out how to get to the flowerpot platform/alcove.
And don't drop your gun. You'll need it.