Stung Treng: See
Most tourists who end up here do so only for a couple of hours before rushing south to Kratie or north to the Laos border. Like anywhere in Cambodia, you could easily spend a day here relaxing by the river, but don't plan on a week. There are a couple of sights to see here, but not enough to seriously keep yourself occupied.
The only meaningful sight in Stung Treng is watching the sun set and rise over the landscape. Great for lounging in a hammock, bottle of Angkor Beer in hand, lazily chatting with your compadres.