A couple of days ago I just answered another posting this... so here it goes for you too:
I would recommend everybody to spend at least a couple of days in the city of Kanchanaburi during your visit to Thailand. There is a lot of history connected to this city. During the World War II the Japanese took at lot of prisoners of war and made them build what is later known as "The Death Railway" across Thailand to Burma - mostly known from the movie "The Bridge Over the River Kwai".
So go pay a visit to the War Cemetary in Kanchanaburi with the headstones of about 7000 allied POWs mainly from Australia, Britain, and Holland who died during the fulfilling of this project. There is a saying that it cost "a life for every sleeper", and besides the many allied soldiers who died, about 80.000 Asians mainly Thais lost their lives here too.
Take a walk across the famous bridge over the River Kwai and get a feeling of what happened here many years ago.
If you really like to dig in the history you may visit the museum right next to the cemetary, or the JEATH Museum at the temple by the river, or you may go visit The Hellfire Pass museum outside the city.
On the more bright side you should spend a whole day by the beautiful seven steps of the Erawan Waterfalls 60 kms north of the city. Hike the waterfalls, and don't forget to bring your swimsuit for a refeshing swim in one of the ponds at the bottom of each step. Easy to get there by the local bus no. 8170 - easy to catch on the main road from about 08.00 in the morning.
The city is now also famous for the Tiger Temple which is located about 45 kms north of the city (on the way to Hellfire Pass) where you may watch the monks walking the tigers and afterwards take your picture while you're padding the tiger on the head. Book the trip at one of the local tour agencies.
Take a traintrip on The Death Railway and enjoy the beautiful landscapes alongside the river, it's both a relaxing and exciting way to get closer look at this wonderful country.
In the evening take a walk along the riverside and have a great meal at one of the nice (and cheap) restaurants there while you enjoy the beautiful sunset over the river and watch the big restaurant-rafts sailing up and down the river with people partying. Later you may go shopping and make a good bargain at the local market located by the railway station. Finish the day with a drink at one of the many places in the street where the guesthouses are located.
In short enjoy the life in a minor provincial city only 125 kms west of Bangkok. Easy to reach by bus leaving every 15 minutes from the Southern Bus Terminal in Bangkok (buy tickets at the blue
ticket counters for aircon VIP bus), price about 100 Baht/person, takes 2 hours. Several nice guesthouses at reasonable prices like 'Jolly Frog', 'Sugar Cane', 'Blue Star', etc. Best hotel is River Kwai Hotel located just on the main street. All accomodations are in walking distance from most of the venues you want to visit - or you may take a tuk-tuk or a samlor (3-wheeled bicycle-taxi).
More info: Kanchanaburi-info.com: destination guide to Kanchanaburi Province, Thailand