The symbol of Cambodia, the five spires of the main temple of Angkor are known the world over. In fact, this is the most resplendent of the Angkor sites, one certainly not to miss even in the most perfunctory of tours.
Built under the reign of Suryavarman II in the 12th century, this temple, along with Bayon and Baphuon, is the very pinnacle of Khmer architecture. From base to tip of the highest tower, it's 213m (669 ft.) of awe-inspiring stone in the definitive, elaborate Khmer style. The temple moat is 1.5*1.3km (1* 3/4 mile) around, and some 90m (295 ft.) wide, crossed by a causeway with long naga statues on each side as railings from the west; in fact Angkor is the only temple entered from the west (all others from the east). Angkor Wat is also the only Angkor monument that is a mausoleum -- all others are temples or monasteries. Angkor's main temple is dedicated to Vishnu.
Approaching the temple, you'll first cross the causeway over the main moat -- restored in the 1960s by the French. Enter the compound across the first gallery, the Majestic Gallery, with some carvings and Brahma statuary, then pass into the large, grassy courtyard housing the main temple. This next causeway is flanked on either side by two small library buildings as well as two small ponds. (Hint: Hop off the causeway and take a photo of the temple reflected in the pond on the right.)
An outdoor staircase sits at the approach to the main temple. From there, you'll enter the richest area of statuary, galleries, and bas-reliefs. The famous bas-reliefs encircling the temple on the first level (south side) depict the mythical "Churning of the Ocean of Milk," a legend in which Hindu deities stir vast oceans in order to extract the elixir of immortality. This churning produced the apsaras, Hindu celestial dancers, who can be seen on many temples. Other reliefs surrounding the base of the main temple show Khmer wars, and corner towers depict Hindu fables.
The most measured and studied of all the sites, Angkor Wat is the subject of much speculation: It's thought to represent Mount Meru, home of Hindu gods and a land of creation and destruction. Researchers measuring the site in hat, ancient Khmer units of measure, deduce that the symmetry of the building corresponds with the timeline of the Hindu ages, as a map or calendar of the universe, if you will. The approach from the main road crosses the baray (reservoir) and is an ascending progression of three levels to the inner sanctum. The T-shirt hawkers are relentless, and the tricky steps and temple height are a challenge to those with vertigo, but the short trip is awe-inspiring and the views from the top are breathtaking. Note: There's a guide rope on the southern face (and often a long line up).
It's a fair walk up to the second level, a flat, open space that overlooks the main temple square, the famed Angkor prangs or parapets on each corner. From here, it's a steep climb (use the staircase with roped handrail on the south side of the temple) up to the third and final level (at time of writing, this level was closed to visitors). There are four large courtyards surrounded by galleries, and balcony overlooks from the base of the prangs at each corner. These high perches are great spots for watching the sunset over Bakeng Hill (though lately, the guards try to get more people down earlier and earlier).
Angkor Wat is the first temple you pass when entering the temple complex, but depending on your guide, you might save it for the evening and head directly to nearby Angkor Thom.