could you please explain what Seishun 18 Kippu is? I don't know what it is and I am really curious how you can cheaply travel around Japan.

Seishun 18 Kippu (youth 18 ticket) is an all-you-can-ride ticket for the Japan Railway Company (JR) trains all over the country. That is about 20,000 km, and good enough to get almost anywhere. The ticket is only 11,900 yen, and is valid for five days if used by one person. The periods of use are the summer break(July-August), winter break (December) and Spring break (March). Although the name says Youth 18, the ticket can be used by anyone. It cannot be used on the bullet trains, and Tokkyu (special rapid) trains. Since the travel cost per day is only 2400 yen, this is a very cheap way to travel. It is ideal if you have a multiple day trip to some place around 300 km away. I used the ticket to go as far as Hokkaido and Kyushu from Tokyo, but that needs a bit of planning since you have to change trains several times. You can get to Kyushu in around 14 hours, with some sightseeing on the way. When our baby was born in rural Niigata and I was working in Tokyo, I used the ticket to go back and see her every weekend. I have great memories traveling with this ticket :-)