Hanayashiki is a small amusement park in Asakusa that has been open since 1953. According to my friends and coworkers it is the oldest one in Japan and also has the oldest roller coaster. Attempting to confirm these claims, I did a little research but was unable to confirm or reject anything except when it opened. At this point it's accepted as fact, as much "common knowledge" is around here. With Japan's history of historical revisionism I think I'll leave it alone before it turns into a huge search.