If you are planning to visit Tokyo, let me recommend the Edo-Tokyo Museum in Ryogoku. I am putting right up in my Top Three Sites, along with Meiji Shrine on Sunday (to watch the equally fascinating traditional wedding ceremonies inside , and the cos-players that assemble outside) and the scenic view from the top of the Metropolitan government's high-rise office building in Shinjuku.
The Edo-Tokyo Museum showcases the history of Tokyo since it was founded (as Edo) in 1590 up to the present day. The highlight are the replicas of historical buildings, almost all of which have been destroyed long ago by fire, earthquake, or war. The museum building itself is also quite impressive. There are many volunteer tour guides that can show you around and offer explanations in many different languages.
PS: Ryogoku is also the centre of the sumo world, which we still have not found a chance to see yet. Well, next season.
PPS: On display in the museum is the Japanese Instrument of Surrender that marked the end of World War Two in Asia. The representative of the Dominion of Canada must have been tired from the years of fighting, because he signed on the line where the Provisional Government of the French Republic was supposed to sign, as a result of which all the following names had to be scratched out and rearranged in hand-writing.



