Even if you're not a fan of military installations, this massive hilltop compound with its citadels, bastions, barracks and ramparts will likely leave a lasting impression. The British began construction of what was then a state-of-the-art fortress in 1690 and, using slave labor, kept refining it for about a century. In 1999 it became a Unesco World Heritage site.
Start your visit by watching the 10-minute video on the history of the island and the construction of the fortress, then wander up to polygonal Fort George to stand on the gun deck, take in the views and imagine the cannon firing all the way out to sea. One floor below are exhibits on the construction of the fortress, life at the fort, slavery, punishment and other topics, along with a recreated barrack room where six soldiers slept side by side in hammocks. For a more in-depth experience, pick up an audio guide at the ticket gate. The fortress sits at the end of a steep 0.75-mile-long road – don't try to walk it; take a taxi or drive.