You gotta look at the stones in front of you, they show the pattern, then turn the stones to the left to that same pattern, like the golden claw puzzle. It's left snake, middle snake, right dolphin
If you look above the gate thats locked you can see there were 3 symbols on the wall on the level above, but the middle one is missing. It's sitting right next to the handle, apparently having crumbled out of the wall over time