This is a relatively small island (approx 4 km by 3 km) next to and connected to the even smaller but better known Don Det, but is more upmarket, quieter and with less of the party crowd found on Don Det.
Note that this is not the same island as Don Khong.
From Ban Nakasang you can reach Don Khon in 25 minutes by longtail boat.
The current "list price" for the transfer is 20,000 kip one way.
Crossing the old French railway bridge from Don Det will cost tourists 25,000 kip and 5,000 kip for locals. However this will gain you access to the Li Phi falls for no additional cost.
The toll is not always enforced on the bridge itself, particularly between late afternoon and early morning, but if you want to visit the falls then you may as well pay here as tickets are checked (but are also available) at the falls themselves
On foot or rent a small bike for 10,000 Kip a day.
Visit the spectacular Li Phi waterfalls (Tat Somphamit) which are on the north west corner of the island. These falls carry the nickname of the Devil's Corridor. They are 2 km west of the French railway bridge that connects Don Det and Don Khon.
There is also a picturesque, small but steep stretch of sandy beach close to the falls, but this is reportedly dangerous to swimmers.
A safer (but less sandy) "beach" exists a little further to the south.
There is another set of falls on the eastern side of the island (known as Khon Pa Soi), which are much smaller in volume and grandeur, but which include a pedestrian suspension bridge over a cataract gorge on its approaches. A small restaurant is situated next to the bridge.
You can often see the rare freshwater Irrawaddy dolphins just off the south coast of Don Khon, and small boats leave from the picturesque village of Ban Hang Khon to give tourists closer views. The cost of a boat is 70,000 kip for a maximum of 4 people. If the boats cross into the waters of Cambodia an additional 20,000 kip is charged.
Ban Hang Khon is itself on the southern end of the old and disused French colonial railway track, which is now a major "road" on Don Khon and which connects to Don Det via the old railway bridge.
Apart from the scenic attractions on the island there is little to do - but that is the major attraction.
Most of the guest houses are on the northern side of the island (opposite Don Det), and many offer hammocks and "lazy" views of the water.
You can cycle or walk around the island, which is often along relatively shady and pleasant tracks.
You can take full or half day kayak tours to see waterfalls and the dolphins. The tours can easily be booked at any guesthouse or travel agent in the main street (full day: 180.000 kips, including breakfast, lunch and ticket to the Khone Pha Pheng waterfalls).
There are a couple of small shops along the "main" road which runs along the northern side of the island. These sell drinks and snacks, and a limited range of other goods.
Souvenirs, including t-shirts, can be purchased from stalls near the Si Phi waterfall.
There are a limited number of restaurants and bars on the island, most located on or next to the islands northern shore.
There are also other eateries located in the more remote corners of the island, but these are infrequent.
Local brews Beerlao and, to a lesser extent, Namkhong beer are available at a number of locations for 9,000 to 20,000 kip for a 640ml bottle.
There are around a dozen guesthouses on the island, almost all located along the "road" on the north side of the island (facing Don Det).
See the get out article of Si Phan Don
Going to Siem Reap (or anywhere in Cambodia): prices are steep (35$ to Siem Reap in almost every guesthouse or travel agent in the island) and service is awful (in the cambodian side, with Paramount Angkor Express). It seems as if there is no other options, though. The bus arrives in Siem Reap at 22:00, not 17:30 as advertised.