The Three Towers -- Guaita, Cesta, and Montale stand along the ridgeline of Monte Titano and are the symbol of San Marino, appearing on the national flag and coat of arms. The walk between them along the Passo delle Streghe (Witches' Path) offers spectacular 360-degree views. Guaita, the oldest, dates to the 11th century and was used as a prison until the 1960s. Cesta, on the highest peak, houses a museum of medieval arms.
The Views -- On a clear day, you can see the Adriatic Sea to the east and the Apennine Mountains to the west. The panoramas from the tower path are among the best viewpoints in this part of Italy -- except, of course, this is not Italy.
Palazzo Pubblico -- The neo-Gothic seat of government on Piazza della Liberta, where you can watch the changing of the guard during summer. The building is open to visitors and the square is the social heart of the tiny republic.
Basilica di San Marino -- The neoclassical main church holds the relics of Saint Marinus, the founder. The interior is austere but dignified, and the square in front offers good views.
Getting Your Passport Stamped -- A small thing, but visiting one of the world's smallest and oldest republics deserves a memento. The tourist office will oblige for a few euros.
The Museums -- San Marino has an unusually high density of museums for its size. The National Museum and Art Gallery in Palazzo Pergami Belluzzi are worth a visit, but the more eccentric offerings -- the Museum of Curiosities, the Museum of Vampires -- are part of the charm.