The Chisor Temple is about 40km south of PP, direction Takeo. To get there, you have to 'climb' about 400 easy steps. During some Buddhist festivals, these stairs are flooded with older people begging for 100 Riel or so, but that wasn't any problem.
Once arrived on top you have the best view over small villages and rice fields. Don't be surprised when you don't see any other tourists. The Chisor temple is still very unknown and private and makes this tourist destination very special. A nice alternative if you compare to the overcrowded temples of Angkor!
It is a nice stop over on the way down to the coast to Kep or Kampot. Tell the taxi to first take Road Nr 2 and then after Takeo take the 3.