Castle Clinton is a circular stone fort built in 1811 on what was then an island in New York Harbour, seven years after Alexander Hamilton's death. It began life as a military outpost defending the young republic from invaders, but New York, being New York, refused to let a useful piece of real estate sit idle. When the army no longer had need for it, the fort became something far stranger: a promenade, then a beer garden, then an opera house and theatre complete with tiered balconies and a towering roof. Later still, it transformed into the New York Aquarium, where visitors once peered at marine creatures through ornate Victorian tanks.

Land reclamation, that relentless expansion of the city outward into the water, eventually wrapped Manhattan around the fort, turning island isolation into waterfront accessibility. Today, a whimsical carousel inspired by the building's aquarium days sits nearby, its thirty luminescent fish spinning amid coloured lights and reinterpreted classical music.

VoiceMap's audio tours use Castle Clinton to trace the fort's unlikely metamorphosis from military necessity to cultural attraction, revealing how a single structure absorbed the city's shifting ambitions and appetites across two centuries.