Prince Shopping Plaza Karuizawa is a large playground for locals and visitors alike near JR Karuizawa Station. There are many brand clothes and shoes, sweets, and cosmetics at discounted prices, and you can enjoy shopping, eating tasty foods, and breathe the fresh mountain air just a few hours ride from Tokyo.
While the Shinkansen fare is not very cheap if you don't have a rail pass, there are also buses from Tokyo and Nagano. Karuizawa is a very peaceful place with lots of opportunities for skiing in winter or walking in summer, but the fall is also a great time to visit.
Find out more about Karuizawa Prince Shopping Plaza.