Welcome to Kitanomaru Park, a stretch of woodland, pond and old stone gateways in the Chiyoda district of central Tokyo, just north of the Imperial Palace. Step in and the city's roar drops away surprisingly fast. The runners looping the palace moat are only steps away, yet here you can stroll, sit under trees and feel almost as if you were out in the countryside. The name tells you where you are. Kitanomaru means the northern enclosure, and this was the northernmost section of Edo Castle, the great fortress of the Tokugawa rulers. Over the next few stops we will follow the park through several lives: a castle precinct, a military post, a public park, and a home for museums and a famous arena. A practical pointer before we wander. Entrance to the park is free, and a marked walking trail circles it in roughly 40 minutes.