Definitely worth visiting if you are in town, the museum has quite a comprehensive collection of artefacts and displays detailing the history of Ratchaburi, from the stone age through to modern days.
Unusually, just about all the exhibits are captioned in English that actually makes sense, really adding to the value of the museum for non-Thais. The section dedicated to dragon jars (the large ceramic pots that you see all over Thailand) is particularly interesting.
The museum also contains a collection of handicrafts and other goods produced locally and a small shop on site has a handful of books and tourist trinkets for sale.
You'll find the museum is at the western end of Ratchaburi near the river, a short walk from the centre of town.