The Eastern Harbour (Itäsatama) is Hanko's signature view — a long promenade of late-nineteenth-century timber villas facing a marina full of summer yachts, with the open Gulf of Finland beyond. The villas were built during Hanko's brief but glamorous period as a Russian and Finnish spa town between 1879 and 1914; about a hundred of them survive, in a wider range of architectural styles than you'd think a town this small could sustain.
A walking trail with discreet information boards loops the harbour and identifies the most important villas; the tourist office sells a more detailed booklet. Several villas are open as restaurants and pensions in summer, which is the easiest way to see one from the inside. The end of the promenade reaches Plaegen Bay and the start of the long southern beach.