If you are a fan of the bakumatsu period or of Sakamoto Ryoma, this small museum is for sure a interesting place to visit.
if you are not so familiar with Japanese history, the bakumatsu period is the period at the end of the Edo era, up to the Meiji restauration, so roughly from 1853 to 1868. It started with the arrival of US ships that requested the opening of Japan. This created a lot of tension in the country, with different factions willing to open the country and other who wanted to expel the foreigners. In that context, a young samurai from Tosa (now Kochi prefecture), as many other, got deeply concerned for the future of Japan. His name is Sakamoto Ryoma, he eventually studied at the newly formed Kobe Naval Training Center then later created a trading and shipping company in Nagasaki, the Kameyama Shachu.
The museum is located in the original building of the company that was restored to look as it was at the end of the Edo period. It is rather small, with only two room that display different artifacts and replicas of items either related to Ryoma or the company. Appart from an explanation sheet in English and the big title of each item, all the rest of the text is in Japanese. However, here is a touch screen monitor in the main room where you can watch several video about Ryoma and Nagasaki, that are all dubbed in English.
It would not be my first museum recommendation in Nagasaki, but as I already said, a good stop if you are a Fan of Sakamoto Ryoma. As a bonus, it is located next to the Sakamoto Ryoma street, that will bring you to the Kazagashira park, where you can find a big statue of Ryoma.