Wat Ban Tham is one of Kanchanaburi's more memorable cave temples, not because it is subtle but because it commits completely to the approach. You climb through the mouth of a huge dragon stairway before entering the cave shrine, with Buddhist images set into the limestone and views opening over the Mae Klong valley as you gain height.
It is a short trip south of town, usually easiest by hired songthaew or private transport. Go early if you can, both for cooler air on the stairs and for a quieter look at the shrine before the day-trippers arrive.