San Diego Harbour San Diego is the southernmost Pacific coastal seaport city on the west coast of California, the eighth largest city in the United States, famous for its warm climate and many beaches, is a very beautiful and liveable city. San Diego Harbour is a natural deep-water port, the main base of the US Pacific Fleet, located in the seaport area of downtown San Diego, with cruise ship terminals, Midway Island aircraft carriers as public museums, submarines and antique sailing ships as maritime museums. Many ships can be seen.