Don Dhet and Don Khong provide a chance to really escape from it all. There are some interesting rapids and waterfalls close to the Cambodian border including a waterfall that is rumoured to be the biggest in Southeast Asia, plus a chance to see the famous Irrawaddy dolphins. The dolphins are best spotted from the south of the island towards the end of the day from December until May. There is also a boat tour available from the end of the pier but remember you will need to pay regardless of whether the dolphins put in an appearance or not.
Bicycles are available for rent, which you can use to explore the entire Don Khong Island, expect to discover plenty of secluded beaches, rice fields and small villages along with some very old temples. The main village is Ban Khong, which is home to Wat Jom Thong, a temple from the Chao Anou period built on the site of a Khmer temple with a hundred-year-old stupa alongside it.
There are also a few villas dating back to the French colonial era and a market, which gets busy early evening. Heading out west from the temple are the rapids and Li Phi Falls. If you are visiting in December then stay around for National Day when there is a five-day boat celebration with additional activities including late night boxing matches.