Phnom Da is a hilltop sanctuary that is best visited by boat from Takeo town.
The hill has caves in the sides which are now used as shrines and on the summit is a large brick and laterite sanctuary which when viewed from a distance looks like a massive nipple. You can step inside the giant nipple and see part of the roof has collapsed and also the remains of what may have once held up a second level inside. Behind the sanctuary there is a great view out over the floodplain to Vietnam. On the smaller hill nearby sits Asram Maharosei, a small rather unusual stone sanctuary that has a very narrow corridor that runs around its interior.
How to get there
Phnom Da can be reached by land or by boat, the latter being the far more scenic option. Boatmen in Takeo will run a trip to Angkor Borei and Phnom Da for $15-25 for the boat -- prices vary tremendously and depend solely on your bargaining ability. A round trip, including sightseeing time is about three hours.