Lara, in a cutscene, will mention something about the Mayan calendar and five unnamed days.  Your mission is to line up four markers.  What you need to do first is go to a panel on the wall and solve a puzzle. 

Again watch for the indicators, and mark the pattern of the tiers.  The first will swing the top tier one way and the bottom tier the other.  The second tier swings independently.  The third tier swings the second and third tiers in opposite directions.  Get the first tier lined up, spin the third tier, and then take care of the second tier. 

When that panel opens, grab the head inside.  It is identical to the one obtained in the temple the first time.  Be sure to go to the left of the panel and grab the weird thing atop the totem pole there.  I wish I could describe it better. 

From here, it is a matter of going to the big circular calendar and putting the tops of those heads on the lever-poles.  Start by turning the panther-headed one first.  You will notice that it turns two circles, an smaller inner one and larger outer one.  What you need to do is spin it so the larger outer circle is its red and gold marker lined up so it is directly behind the red and gold marker on the outermost circle.  This will actually click when it is in the right place, so don’t move it any further. 

Now, go to the other lever.  You will notice that the outermost ring moves, but don’t worry, it will move back.  Just move it as far as you can, and a small circle will come out like a cover. 

Go to the panther headed pole again, and spin it until the red and gold marker is line up in front of the gold marker on the smaller circle.  Then head back to the skull-topped pole and move the cover so it is back in place. 

A huge metamorphosis will take place, and you might not recognize that area now, but you are about to go to it.  Go back to the ledge on the left of the cliff, and just hang off.  All you need to do is release several times until you are on the ground.  Go back to your motorcycle, and go back through the pressure release point that is the gate.