I agree with berni23 and Degolasse.
Kanchanaburi Province is actually very big and there is more to it than just the “bridge” and war cemeteries. It's the third largest province in Thailand. The landscape has both mountains and plains. Natural beauty includes the waterfalls and national parks. You can go bamboo rafting, elephant riding, trekking into the forests and a lot more. I would suggest you to go there by train and strongly suggest exploring the area around The Death Railway, The JEATH War Museum, Hell fire Pass Memorial, Wat Tham Sua, Erawan Waterfall and Sangklaburi. I'm sure that you will not disappointed for these 4 days Kanchanaburi trip.