A few kilometers outside Kampot, on the road to Kep. Left side, you'll see a sign.
Park a the Wat (Buddhist Temple), look around, and go up the stairs.
You'll probably have a guide (give them a thousand riel or two) and there's a few caves, very small, at the top. Good for a half hour stop. Won't tell you any more, you'll just have to go yourself. (no English spoken)