The Owl Tree is a large tree located in ThunderClan's Forest territory. Oddly, although a ThunderClan warrior says the Great Sycamore is the largest tree in the forest, the Owl Tree is portrayed as being much bigger.
The Owl Tree is one of the two hunting locations where there is something else to do besides hunting. The Owl tree can be climbed, with you either falling off midway or making it to the top. Climbing the Owl Tree will give you a 20 EXP boost to every member in your party.
Graystripe is found here during an event in the Original Game.