The Tomioka Silk Mill was built during the Meiji Restoration. As you may know the Meiji Restoration refers to Japan in the 2nd half of the 19th century. Japan had been living in isolation for centuries. Due to military incursions by the Americans Japan came to realize that they needed to catch up fast with the rest of the world. While the general industrial advances are covered by the Sites of the Meiji Industrial Revolution Tomioka is focused on one specific factory for silk production.
The factory itself was built with support from French engineers. Walking around it does have a colonial feel to it, especially with regards to the living quarters. The site also encompasses three other locations related to silk production and tries to provide a full picture. As these are further off, I did not manage to visit, though.
Operations at the site ceased rather recently (1989) and most of the original equipment was preserved. So the site feels authentic and complete. With the very unique focus on industrial silk production I think this is a valuable addition to the list, although a niche one.
Getting There
I visited Tomioka as a stop over on my way from Tokyo to Kanazawa. I had to change in Takasaki where I deposited my luggage at the station. Be aware that the railways from Takasaki to Tomioka is not included in the Japan Rail Pass so you will have to get a separate ticket. From Tomioka Station you can walk.
I did not investigate how you can visit the other more remote components of the site. If you are visiting as part of a day trip from Tokyo you should be able to visit at least one more.