The site where the Treaty of Peace and Amity between the United States and Japan was signed in 1854 was the former British Consulate General, the museum's predecessor. The museum houses a collection of valuable historical materials related to the opening of Japan to the world and the opening of Yokohama Port. It is said that Commodore Perry and the shogunate met under the "Tamakusu tree" in the courtyard, which still remains to this day. In 2009, the mascot character for the 150th anniversary of the port's opening, "Tanemaru," was designed as the "spirit of this Tamakusu tree." The adjacent Port Opening Plaza also displays Japan's oldest brick manhole and sewer pipe.
