Jikan Ryokou (the sign is in Japanese 時間旅行, it means "Time Travel") is simply wonderful. It's a tiny 12-seat joint in the back streets of Nakano, an area full of small drinking dens. The owner Asai-san is in her late 50s and opened the place about twenty years ago..she was being coy about dates and her age as bar mama-sans often are.
As you can see from the video below, the walls are covered in classic rock album covers as well as jazz records. In one night there I heard John Coltrane, the Rolling Stones, Bob Dylan, Cannonball Adderly and as I was leaving late at night I think she was pulling out some Mozart. So it's not exclusively a jazz spot but most music geeks I know would have no problem with any record in her huge collection.
Station: Nakano Station - JR Chuo, Sobu lines, Tozai Subway Line
Distance from station: 6-9