Castillo San Cristóbal

The hill it stands on was once called the Cerro de la Horca — Gallows Hill. The Spanish renamed it for Saint Christopher and built the largest fortification in the New World on top of it. Construction began in 1634; the fortress took 150 years to complete and covered 27 acres when finished. In 1797, its defenses helped repel a British invasion force of seven thousand soldiers. In 1898, its guns fired the first shot of Puerto Rico's entry into the Spanish-American War. The Garita del Diablo, the "devil's sentry box," still stands at the waterline — and local tradition holds that soldiers disappeared from inside it, though the story passed down here is that at least one of them simply ran off with his girlfriend.