We absolutely loved the War Museum.
It is 50 Baht entry and you get access to the whole museum which is actually quite large. We spent around 45-60 mins in total.
There are artefacts, vehicles, weapons and lots of other items kept from WWII and there is an abundance of information on each section. There is history of Thailand during WWII which I didn’t know about before I came, and there’s also some other info on the Bridge over the River Kwai.
Would absolutely recommend visiting here if you are coming to Kanchanaburi.