Peru -- Primarily Machu Picchu (Dec 2010)

A walkway between two walls. The wall on the left is part of a building. I'm not sure if the one on the opposite side is a building or a retaining wall.

They consider the walls in the city were built in about there different quality levels, with the wall on the left side of this photo being on the highest quality. The theory is that the highest quality walls represent the buildings with the highest-status purposes, such as temples and royal residences.