The Edo Tokyo Open Air Architectural Museum is a real gem and I don't really know why it's taken me 4 years before visiting it the first time. The grounds of the museum are spacious, right in the middle of Koganei Park, and you can wander in and around typical Japanese buildings from various periods and experience how Japan was like at that time. The buildings include farmhouses, private residences and a complete downtown area with local shops and a public bath—I really recommend to visit.