The main attraction of 130-sq-km Khao Phra Wihan National Park (อุทยานแห่งชาติเขาพระวิหาร) is Khao Phra Wihan ('Preah Vihear' in Khmer), one of the region's great Angkor-period monuments. Though it sits just inside Cambodia, it's easiest to reach via Thailand. Hugging the edge of a cliff on the brow of the Dangrek escarpment and accessed via a series of steep stepped naga approaches, the large, unrestored temple complex towers 500m above the Cambodian plains below offering both evocative ruins and stunning views.
There's no way to guess when access to the temple from the park (previously the Cambodians charged 200B and the Thais collected another 5B) will resume, though the small core section of the park, full of razor wire, bomb shelters and soldiers, above Pha Mo E-Daeng cliff has reopened. It's a nice place to visit, but it's probably not worth a long trip and definitely not worth the inflated 400B foreigner entry fee.