I travelled solo through Japan for little over three weeks. Traversing the country by bike, speedy bullet train, boats and busses, I've had a really good time discovering Japanese culture which I feel in love with. The people are really friendly, and go out of their ways to help you. The food was great, so was the whisky, sake and the countless drinks from the vending machines.
I can not recommend Japan enough, it's a must see destination. It might be challenging to navigate with the language barrier as not a lot of people are profficient enough in English. However, sign language and pointing and gesturing things helps out! Make sure to read Juan Buis's wonderful articles about Japan.
I've collected big & small lists of things to do when you visit. Feel free to reach out if you have any questions about a specific place.