When you visit Kanchanaburi city, the town of the bridge over the river Kwai and the war cemetery, you could consider a visit to Khao poon cave (also written as Khao Pun). The place is also known as Wat Tham Khao Pun. Wat is the Thai word for temple. I know that most people stay only briefly in Kanchanaburi. They visit just the Bridge and the war cemetery. Some visit one of the few museums too, but hardly anyone visits the second war cemetery at Chungkai, which is a few kilometers from the other war cemetery in town.
The cave is not a huge one as many other caves in Asia, but definitely worth to visit. I would call it a mixture of cave, temple with Buddha statues and war history. This is because there is a part at the end where you come out of the cave where old pics of POW’s, the Death Railway and the bridge are shown.
Inside the cave there are several rooms. Not all of those rooms have an exit. Some parts are quite narrow and dark. You need both hands at some points and might get your clothes somewhat dirty. There are many different Buddha’s in all kinds of positions to be seen. For more info you can look here: travelfish.org.
The entry price is 30 baht p.p. Opening time is 8:00 am to 5:00 pm.
How to get there?
When you stay in Kanchanburi’s one and only tourist road, you walk in opposite direction of the river Kwai bridge. This means you go to the cemetery. Follow that road and turn right after the school which you see on your left hand side. At the traffic light you go straight over the bridge, followed by another bridge. At the T junction you turn right again and follow that road. You will cross the railway and soon you’ll see the Chungkai war cemetery. Immediately after Chungkai, the road goes uphill and on top of that hill lies Khaopoon cave on you left hand side.
It sounds far, but it’s not realy that far. I wouldn’t recommend to walk it though. You can rent a scooter for less than 200 baht per day ($5) or a bicycle for 40 baht ($1) and go to the cave and/or Erawan waterfalls.
Khaopoon cave is worth a visit when you are in Kanchanaburi. An impression video can be seen here https://www.youtube.com/watch?v=GLBAuVLiUL8&feature=youtu.be