The only way I can possibly see getting that treasure is breaking a bridge that has an opening into that area, but just getting down there safely when the bridge is breaking is completely based on luck. After that, I have no idea how you would get out.
There are two bridges that overpass the passage that leads to the treasure. One makes an arch, the other (the second one) goes straight down. When you get to the second bridge, press space, and some parts will unhinge, the top left of the bridge will fall and will connect to the passage below. You just need to back up, calmly, and collect the treasure.
