When you think of Cambodia, visions of tranquil beaches probably aren't the first thing that come to mind, which is a shame. It isn't much when compared with the quality and quantity of beach living in nearby Thailand, or even along the coast of Vietnam, but the southern coast of Cambodia boasts some fine sandy stretches worthy of putting your feet up for a few days, especially after some heavy-duty temple touring or bouncing around the roads of rural Cambodia.
Rte. 4, which connects Phnom Penh with Cambodia's only port at Kompong Som, or Sihanoukville after the former king, was built by the United States to facilitate Cambodian trade and the influx of aid starting from the mid-1960s. Just adjacent to the busy Sihanoukville port, you can find some lovely little beach areas, most of which are speckled with budget bungalows and groovy bars owned by Western expatriates. The town of Kampot is a lazy little river town, just a grid of mostly colonial-style houses along a quiet, lazy river, but another good place to kick back. You might also visit nearby Kep, which was a French colonial vacation spot whose 1950s/1960s-era villas lay in ruin. It's also a seafood mecca, and worth visiting just for its Kep crab in Kampot pepper. Connections by bus with Sihanoukville are convenient, and many choose to do this region in a rented vehicle or even by affordable local taxicab. So, if you're stuck in Phnom Penh for a few days waiting out a Vietnam visa, hit the beaches. You'll be surprised.