The place where the Convention of Kanagawa was signed in 1854 was the former British Consulate General, which was the predecessor of the museum. Valuable historical materials related to the opening of Japan and the opening of Yokohama are collected in the museum. It is said that Admiral Perry and the Shogunate met under the "Tamakusu Tree" in the courtyard that still remains. The mascot character "Tanemaru", the 150th anniversary of the opening of the port in 2009, was designed as this "Tamakusu tree spirit". At the adjacent Yokohama Port Opening Square, Japan's oldest brick manhole and sewer pipe are also on display.