On my last trip to Cambodia in 2012, we only had two days in Seim Reap, so our travel agent set my wife and me up with our own tour guide and driver for a day and he took us to Angkor Wat, Angkor Thom, and Ta Phrom in one day. It was a little busy, but not that rushed. The next day we just had a driver, so I had him take us to Bantey Shre. If we had more time I would have gone to the Rolos temples for one day and a day on our own at Angkor Wat. You need a guide for most to the temples. You need to spend at least two days in Phonm Pen as well. Climbing the steps of the temples is adventurous, but they have put up wooden steps in many places. My favorite place is Pimenakes in Angkor Thom. Pardon my spelling for the Cambodian names. My first trip was in 2003 with Intrepid. There were only 8 in the group, but that was during the SARS scare. You get close to the people with Intrepid, solo travelers are welcome (my wife and I were the only couple in the group), and you sleep in 3 start hotels.