Zhenhai Fort, at the mouth of the Yong River about twenty kilometres northeast of central Ningbo, was built in the Ming dynasty to defend the river approach against Japanese pirates (wokou) and was repeatedly strengthened as successive dynasties recognised the strategic importance of Ningbo's main waterway. The fort's most significant historical moment was the Opium War engagement of 1841, when British forces captured it and occupied Ningbo — one of the first occupations of a Chinese city by a Western power.
The fort and its surrounding walls are remarkably well-preserved, and the museum within documents the Opium War battles along the Zhejiang coast in detail that goes beyond the usual patriotic narrative to include military analysis, personal accounts, and material evidence from the engagements. The coastal views from the ramparts over the river mouth and the East China Sea are good, and the combination of Ming fortifications, Qing cannons, and colonial-era military history gives the site an unusually layered quality. The fort is reachable by subway from central Ningbo.