I've beaten the game over fifteen times, and I have all of the rewards except for the Gold reward in Peru.

I would be very grateful if someone would point out where about it was on the level, or how to reach it.

its the 4rth stone ball you put in the center floor plate of the puzzle.

quote Neopets

I've beaten the game over fifteen times, and I have all of the rewards except for the Gold reward in Peru.

I would be very grateful if someone would point out where about it was on the level, or how to reach it.

As Darklight says. The game sort of gives a hint. When Lara grabs the rope taking "the high road" back the message about how to move up and down the rope is displayed.

On a small ledge above the huge pit,turn and line up lara
precisely with the dangling vine.jump,grab vine turn lara on the vine to face broken ledge on opposite side of the pit to the left/leftmost of 3 ledges.
climb up until lara is roughly level with the narrow stone shelf running along the entire wall.swing as high as possible
jump and grab stone shelf,allowing you to jump up to grab the narrow shelf.climb left to an opening in wall.jump accross one gap on the way,pull up into the doorway,enter go up ramp to the right.4th stone,shove it to send it on its way.
follow and drop onto the ledge below the opening.from there take a huge running jump to statue on right.climb down the ladder to floor roll sphere onto center pad,so there are now x2 spheres there.this further raises the pedistal at the center revealing the GOLD REWARD..INSIDE..