Peru: Mountain caves:

At the end. locate the pole that moves when you swing on it, then as its swinging jump off and you should land on a ledge. Shimmy across and climb up. Eventually you will reach the top. The rewards awaits you.
Lost Valley:

Hard to explain, er...cross the bridge above the waterfall. If you want to check, fall of the bridge and you will die in the rapids. Crawl across the wall with the machinery. Be careful, 2 bats will chase you. Pull up into a stone room and a switch will be there so pull it. A gate opens somewhere underwater. Once you have stopped the waterfall at the beginning, dive in what was once the raging river. The reward is in a cave under the water.
Tomb of Khamoon:

At the end, there are a handful of rooms. Once the gate is open, look at the gate. To the right is a room. Pull the block that was barring the way towards the gate. Climb on and grab the crack. Follow the obvious route and balance on the top of th cartouse (poles). Jump across to the room on the other side and a Mummified Cat relic awaits.

Sorry I only know where 3 are but I'll inform you if I find some more. Take care and may you have a nice day! :)