Preah Pithu is an interesting complex of five temples in Angkor Thom, which seem to be scattered randomly throughout the forest on this short .5 mile run. It seems longer because you are exploring around the temples and have the opportunity to explore inside. The trail is not marked but obvious when you run to the back of the tourist eating shanties. You first encounter Preah Pithu V which is just an entrance platform. Past that and to the left is Preah Pithu Y, a temple you can climb up into, but past that there is not much to explore. Run around the back of this temple and through the forest where you can see another small temple to the right, Preah Pithu X.
The trail continues to the back of Pithu X, but loops back to the group to encounter Pithu U and Pithu T as you head back out to the tourist shanties. This is another well shaded trail that is great to do after breakfast at the tourist restaurants. Not many people venture out here so it is likely you'll have the temples and trail to yourself.