Kanchanaburi is one of the larges provinces in Thailand. From my hometown, the province capital Kanchanaburi, I have to drive about 230 kilometers to the North. Sangkhlaburi is a very small town. A huge part of the inhabitants are refugees from Myanmar. Most of them don't even speak Thai. I can recommand this place to any visitors.
However, if you need night activities you'd better stay in a larger town or bring your partner along 
Here you can't buy a Coke or a bottle of water after 8 p.m. But if you like nature, walking or trecking then you're in the right place! Here I show you some nice pictures.
Unfortunately this in NOT mine
The lake is artificial. It's origin is the Vajiralongkorn Dam in Thong Pha Phum. For more information please go to wikipedia: http://en.wikipedia.org/wiki/Vajiralongkorn_Dam