Castle Island is a historic site located in Boston Harbor, Massachusetts. It is home to the Fort Independence, a star-shaped fort built in the 19th century. The island offers scenic views of the harbor and the city skyline, making it a popular destination for both locals and tourists. Visitors to Castle Island can enjoy walking along the waterfront paths, picnicking in the park, and exploring the fort. The area is also known for its beaches and recreational activities, such as fishing and swimming. Castle Island is accessible by car, bike, or public transportation, making it a convenient spot for outdoor enjoyment.