As for sightseeing spots in Tomioka, there is the Tomioka Silk Mill which is a factory that has contributed to Japan’s modern silk production. It is known for having been registered as a World Heritage site in 2014, so if you are visiting Tomioka make sure to visit. Aside from that, there are spots such as Myogi-jinja Shrine, Gunma Safari Park, and Rakusan-en Park. Shimonita is also known as a production area for green onions and konjac, so give them a try if you have a chance.
For traveling through the area, we recommend using the Joshin Dentetsu Joshin Line. Joshu-Tomioka Station is the nearest station to the Tomioka Silk Mill; you can access it from each major city by taking the Joetsu Shinkansen to Takasaki Station and then transfer to the Joshin Dentetsu Joshin Line. From Tokyo the total travel time is about 1 hour 40 minutes.