Phu Nam Ron
From Kanchanaburi you can take a local bus for 70B, it departs at 10:30, 12:00, 14:00 and 16:00. The journey takes about 2 hours, tickets are bought on the bus. You can take a Minibus as well, for 100B. They depart at 9:00, 12:00, tickets have to be bought at a booth (probably). You can ask at the information desk for up-to-date information, they are friendly and speak relatively good English.
It's very small, so everything is in walking distance from where the bus drops you off.
Cross over to Myanmar.