Fort Jefferson is the largest brick masonry structure in the Americas, built on an island in the Dry Tortugas, Florida, 68 miles west of Key West in the Gulf of Mexico. Constructed with over 16 million bricks beginning in 1847, this massive pentagonal fort spans 16 acres and served as a Union stronghold throughout the Civil War. The fort housed notable prisoners including Dr. Samuel Mudd, and was proclaimed a National Monument in 1935, later becoming part of Dry Tortugas National Park in 1992. The surrounding islands provide excellent snorkeling in shallow waters and attract over 299 bird species, making it a unique destination combining history and natural beauty.