Tomioka Silk Mill

Tomioka Silk Mill was added to the World Heritage site List as a cultural site on June 21st, 2014. A lot of Japanese are visiting there.
Tomioka Silk Mill is known as Japan’s oldest modern model silk reeling factory. It helped Japan develop.

It is not in Tokyo, but in Gunma Prefecture. If there is free time for you, i recommend you to visit there. It will take about 2 hours from Tokyo Station to Tomioka Silk Mill by train.

http://worldheritagesite.xyz/tomioka-silk-mil/