Castillo San Cristóbal (Fort San Cristobal), San Juan (must see)

Standing guard at the eastern gate, north of Columbus Square, is an imposing 18th-century fortress, called San Cristóbal. Contrary to her sister, El Morro, which was designed to protect from attacks by sea, the San Cristóbal Fort guarded the city against the enemy approaching by land, for which purpose it created a crossfire with El Morro over the bay. The citadel construction began in 1634 and was meant to strengthen the Spanish position in the face of imminent English and Dutch invasion.

The fort was named San Cristóbal in celebration of the Spanish victories which enabled ejecting of the English and Dutch interlopers from the island of the same name in the Lesser Antilles, which was then part of the insular territorial glacis of Puerto Rico.

When finished in 1783, the Fort San Cristóbal covered nearly 27 acres of land and practically wrapped around the whole of San Juan, with the entry to the city sealed by the San Cristóbal's double gates. After almost 100 years of relative peace, about a third of the fortification was demolished, in 1897, to help ease the flow of traffic in and out of the walled city.

The Fort San Cristóbal is now a listed National Historic Site. It is particularly worth visiting as the largest fortification ever built by the Spanish in the New World, where the first shots of the Spanish-American War were fired. If you're a keen photographer, San Cristobal is a goldmine of panoramic views of the coast, from Old San Juan to Condado and beyond.

Tip:
Guided tours by local rangers visit the extensive tunnel system connecting various sections of the fort. There is an exhibition of military clothing. Be sure to visit the overlook for the Devil's Sentry Box ("Garita del Diablo"), from which, according to legends, soldiers mysteriously disappeared. Tickets to San Cristobal or El Morro can be used to enter either of the forts.