While the cave here is nothing amazing, the access along a viaduct of the Death Railway provides spectacular views over the surrounds, with a river sliding by well below you.
The train stops here to allow passengers to jump off, take a look around and buy various touristy knick-knacks. But if you visit at any other time, chances are you'll have the cave and viaduct totally to yourself.
Tham Krasae and the viaduct are well off Route 323 and are marked by signs -- if you don't have your own transport be prepared to hitch from Route 323. If you are travelling by train, the stop here is more than enough to see the cave and admire the view.