Flip the last switch and the last door will open, so go in and get to the last puzzle for this level.
Go through the exit, you'll need to get upstairs.
You'll need to pull the box on the right side then flip the switch to raise the grates (well, that was easy).
Now go right inside and admire the ... spikes.
Pull the lever and now make sure you're fast. Of course if you don't make it from the first time I suggest you jump into some spikes, there's a checkpoint right after you pulled the lever.
I maked the path which you need to follow on the picture. However, you need to be fast and don't make any mistakes since pretty much everything it timed.
And in the end you should have the last lead bar. Phew, that was hard.
Additionally you can pull the blocks on the right with the grapple, there's an artifact inside and then figure out a way to get there (you'll need to do pretty much everything a second time and instead of going left for the lead bar, go right).
Now get back to the statue, get close to the hand (but DON'T step on it), and use each bar on it. They will turn into pure gold. Sweet.
Now put those into the holes on the statue and the exit in the pool will open. Tada.