The main stadium in Phnom Penh, it has a seating capacity of 50,000 and built in 1964. During the reign of the Khmer Rouge, the stadium was used as a site for executions by officials under the administration of Lon Nol.
These days, the stadium and surrounding grounds are a popular place for morning and afternoon aerobics, lead by instructors. The parking lots provide room for hundreds of young khmers to have chaotic bare-foot soccer matches. Other facilities include an Olympic sized swimming pool and indoor volleyball court, another popular sport in Cambodia.
Here is a pretty interesting anecdote about the Phnom Penh National Olympic Stadium, involving Australia:
The stadium played a small part in the 1966 FIFA World Cup. Unexpectedly, North Korea faced Australia in a qualifier. Because North Korea lacked diplomatic relations with most countries, finding a suitable venue for the match proved difficult, until Head of State Norodom Sihanouk, an ally of Kim Il-sung, said the matches could be held in Phnom Penh. The matches attracted 40,000 fans, with Sihounouk decreeing half would cheer for Australia, while the other half cheered the Koreans. The matches were held on 21 November 1965 and on 24 November 1965 with North Korea winning both (6–1 and 3–1). Because South Korea and all African teams had withdrawn in protests against FIFA, North Korea were thus directly qualified to the final tournament, where they reached the quarter-final. – Source: http://en.wikipedia.org/wiki/Phnom_Penh_National_Olympic_Stadium
Below is an image of a single person sitting on the stadium seats: