First set up your truck and then go to the Excavation. Next when you started the race switch your map on and then go to the loop right before you jump to the straightaway. When you are there you will see a temple, go around the temple until you see the brightest side. when you find it you will see a opening, go in side of it but before you do go to the right or the left to get in, you can't go stright. To get out push "H" to activate the helicopter.