Three Pagodas Pass (ด่านเจดีย์สามองค์ Darn Chedi Sam Ong) is on the Thai-Myanmar border, but accessible to foreigners only from the Thai side. It is between Sangkhlaburi in Thailand and Payathonzu in Myanmar.
Three Pagodas Pass was for centuries on the main land route between India and South East Asia. The strategic location was last exploited during World War II by the Japanese, who used POW labour to build the infamous Death Railway to ferry supplies to Burma from Bangkok.
The Thai side of the pass consists of the three smallish chedi, a couple of shrines, a market oriented around Burmese goods (carved wood, gems, textiles), and the border gate to Myanmar.
In Myanmar you can take a look at a few temples as well as a market. None is really in any way very special. However there is one temple that is up on a hill, from where you get a great view across the border.
Burmese wooden furniture, jade carvings, and textiles are popular purchases.
On the way from Sangkhlaburi there is a concrete bridge. Down to the right is a small restaurant on the river. There is also another restaurant on the roadside just past this on the right hand side that does meals for around 50 baht per plate.
The area around the pass has occasionally been the site of skirmishes between the Burmese Army and various Karen and Mon rebel groups. Any such activity will mean that the pass is closed, so risk to tourists is non-existent.
There are only two ways: either back to Kanchanaburi or by crossing the border to Payathonzu in Myanmar.