The AOPs and trail are marked on Open Street Maps which is how I found them. I would suggest approaching from the South from the Morning Walker Garden, and then either continuing North after the cache or doubling back. Note if you pass a set of abandoned Mahjong tiles, turn back, you are not on the trail as I found by the hard way.
Apparently there is a tunnel network which starts in the large hole, however I wasn't brave enough to explore it.
http://gwulo.com/node/5641