Preah Vihear temple is the second and last Khmer monument that is a UNESCO World Heritage Site and is found 1 and a half hours from Anlong Veng. We found things as marvellous as those at Angkor without being hemmed in by hordes of tourists.
Then we found the tomb of Pol Pot, Ta Mok's house, and the last places where the Khmer Rouge lived. Anlong Veng was the final bastion of the dictatorship. You can go trekking in search of their ghosts (better with a guide) which can easily replace the classic visit to the killing fields of Phnom Penh.
Anlong Veng taught us a lot about Cambodia, about its past and its present, and finally gave us a picture of a Cambodia without tourism or capitalism - a real change of scene after Siem Reap and Phnom Penh.
Finally you should know that Anlong Veng is 15 minutes by car from the Choam border crossing with Thailand. This small town could well be your entry or exit point in Cambodia.