Roosevelt Island, located between Manhattan and Queens in the East River, has undergone numerous changes both in name and use and been passed to numerous owners in its recent history.

The "island under Manhattan" typically refers to Roosevelt Island, a narrow, two-mile-long island located in the East River between the island of Manhattan and the borough of Queens. While it is physically separate, it is administratively part of the borough of Manhattan. In 2026, it remains a "hidden gem" for residents and tourists alike, famous for the Roosevelt Island Tramway, which provides a stunning aerial view of the skyline for the price of a standard subway fare. The island has a rich, multifaceted history, once serving as the site for hospitals and asylums, including the hauntingly beautiful Renwick Ruin (a former smallpox hospital) and the Octagon tower. Today, it is a peaceful residential community featuring the Franklin D. Roosevelt Four Freedoms State Park at its southern tip and the Cornell Tech campus. Its unique "under-the-bridge" geography—nestled beneath the Queensboro Bridge—makes it one of the most distinctive landscapes in New York City.