Preah Vihear is perched on a hilltop with a commanding view of its surroundings. Predating Angkor Wat by 100 years, the history of the temple/fortress is somewhat unclear, but it is known to be dedicated to the god Shiva and thought to have been constructed in the reign of Suryavarman I (1002-50), with further significant additions by Suryavarman II (1113-50).
Long considered to be inside Thailand, King Sihanouk of Cambodia claimed the temple on the basis of French colonial maps. The Thai government agreed to submit the dispute to the International Court of Justice, which in 1962 issued a controversial ruling awarding Preah Vihear to Cambodia - which soon after plunged into civil war. The temple was open to the public from Thailand (although unreachable from Cambodia) until 1975, when it was occupied by the Khmer Rouge (whose rusting artillery guns still litter the area). It re-opened from the Thai side in 1998, and in 2003 Cambodia completed the construction of a long-awaited access road allowing Cambodians to visit the temple.
If this is out of your budget, the nearest town of any size is Kantharalak, which can be accessed by frequent public bus in 2 hours or so from the nearby towns of Ubon Ratchathani and Si Saket. For the last leg of the trip (34 km), however, you will have to hitchhike or charter a songthaew/tuk-tuk/moto taxi.
At the entry gate into Khao Phra Wiharn National Park, you will have to pay a 200 baht entry fee (Thais 20 baht); note that the park is open only from 08:00 to 15:30. The road ends at a large parking lot, the final leg (less than a kilometer) into Cambodian territory you will have to cover on foot. At the Thai immigration post you'll be charged an additional 5 baht for a second ticket, and you'll also have to show your passport - they'll take a photocopy, but no stamps are issued and no visas are needed. After the road ends, walk over the smooth rock surface to the entry gate and pay another 200 baht fee (this one to enter Cambodia) and get your ticket punched, and now you can proceed to the ruins.
You can also reach the place on a three days motorbike trip from Kompong Thom (view details)
The only way to get around is on foot. The 500m elevation and the resulting breeze provide some relief, but it's still a hot and sticky 120m (vertical) up the hill.
From the Cambodian side, you can hire a motorbike-taxi to take you up the steep ascent to the temple.
The Thai and Cambodian paths join together at the bottom of the slope (north end of the adjacent map), and from here the only way is up.
There's one more sight worth seeing in the area, accessible only from the Thai side:
There are ramshackle assemblages of shacks at both the Thai parking lot and the Cambodian base of the hill, as well as all the way along the path up the hill in the temple area itself. These sell not only the expected T-shirts, postcards and cans of Pepsi, but premium cognac and cigarettes by the carton as well: it's tax-free shopping for the Thais! As foreign visitors are few, expected to be besieged by little boys and girls shouting "Hello" and hawking postcards, but they usually take the hint after a couple of "bye-byes".
Places to eat are rarer on the ground than drink stalls, although there are some pretty basic grill stalls towards the end of the Thai parking lot shopping shacks.
For more selection and a semblance of hygiene, there are a number of roadside restaurants on the Thai side before the park entrance, along the road from Kantharalak.
Drink stalls are ubiquitous along the trail.
There are only very basic accommodation options in the immediate vicinity.
Cambodia: the village at the foot of the mountain provides two or three very basic "guesthouses" in simple wooden shacks. There is also a wooden, very basic guesthouse (shower and loo outside) at the bottom of the steps, where the locals live. Shower is from a barrel of rain water and a bucket. Very, very basic but very clean. Electricity from 6pm to 10pm. (May/2008)
Thailand: the nearest place with a variety of accommodation is the town of Kantharalak (approx. 30 km), which is also the nearest place with direct bus services to Bangkok, Si Saket, Ubon Ratchathani, etc.
More distant Thai-side possibilities are the towns of Si Saket (approx. 95 km, and nearest train station), and Khu Khan (approx. 95 km, and most convenient place to stay near the border if travelling to/from Anlong Veng); and the city of Ubon Ratchathani (approx 120 km) - however, the most direct access to all these places is via Kantharalak.
Land mines remain a real danger in the area, although the temple itself and the access paths have been painstakingly cleared by the HALO Trust. Stay on the beaten path, don't venture into any vegetation which has not been cleared recently, and heed the red warning signs, painted rocks and strings marking the limits of the demined area.
The cliffs are steep and no provisions are made to protect you from your own carelessness. Keep a very close eye on children.