If you get tired of walking around Ueno, one of the most crowded tourist areas in Tokyo, I would recommend you visit Kaneiji Konpon Chudo Temple. It is not big and gorgeous, but creates a peaceful atmosphere with fewer crowds. The way to the temple also reveals some beautiful architecture with a lot of greenery.
Konpon Chudo was established in 1698. However, it burned down during a civil war and was then reconstructed in 1879 (during the Meiji Period). It is built of dark brown wood and has a relaxed ambience. Buddhist statue treasures are housed inside the hall.