Spectacle Island is a 105-acre island in Boston Harbor,  4 miles (6.4 km) offshore of downtown Boston, Massachusetts. It is part of the city of Boston. The island has a varied history, and today is a public park with a marina, visitor center, cafe, lifeguarded swimming beach, and five miles of walking trails,  forming part of the Boston Harbor Islands National Recreation Area. It is served all year by ferries from Boston, and on weekends and summer weekdays by a shuttle boat to and from nearby islands.  
The island was initially composed of two small drumlins connected by a spit, with an approximate size of 49 acres (200,000 m2). The name is believed to derive from its then-resemblance to a pair of spectacles.  However, dumping of trash and dirt, together with subsequent landscaping, have resulted in a significantly larger island with a permanent size of 85 acres (340,000 m2), plus an intertidal zone of a further 28 acres (110,000 m2).
The island is now composed of two artificial earth mounds, terraced with retaining walls, roads and newly planted vegetation. With a height above sea level of 157 feet (48 m), Spectacle Island is now one of the highest points on Boston Harbor.   The island's inner harbor acreage is 114, with 85.5 upland acres and 28.4 intertidal acres. 
Starting in the early 19th century, the island was used exclusively for its relative remoteness from Boston. Two hotels were built in 1847, only to be closed by police ten years later when it was discovered they were used for gambling and other illicit activities.
A horse rendering plant was built on Spectacle Island in 1857, followed by a city trash incinerator that remained active until 1935. When the incinerator closed, trash was simply dumped on the island for the next thirty years. A bulldozer was supposedly swallowed up by the trash sometime during the 1950s. The island remained a smelly, leaking dump until the 1990s.  
Two sets of range lights were erected on the island by the United States Lighthouse Service. The Spectacle Island Range Lights were established in 1897 to mark the last leg of the channel into Boston itself, past Governor's Island; they were not long-lived and were discontinued in 1913.  The Broad Sound Channel Inner Range Lights were first lit in 1903 and discontinued around 1950; these indicated the middle leg of the trip.  No trace of any of these lights remains.
When the Central Artery/Third Harbor Tunnel Project, or the Big Dig, began work in Boston in 1992, some of the project's excavated dirt and clay was used to resurface the island. The island was covered and built up by dirt, capped with two feet of clay, and covered with two to five feet of topsoil. Thousands of trees were planted, and paths, buildings, and a dock were built.
Spectacle Island is accessible to the public either through a ferry from Long Wharf or to private watercraft at the island's marina. Ferries run hourly from and to Boston as well as from and to Georges Island.  The marina was closed for almost two years in the late 2010s due to repairs required as the result of a storm in the winter of 2015. As of July 2017, the marina is open and public moorings are available.
- Spectacle Island is featured in the video game Fallout 4.
- The island plays an important role in the novel Zodiac: An Eco-Thriller, by author Neal Stephenson.
- Spectacle Island is mentioned in the book The Speckled Monster by Jennifer Lee Carrell. It is described as a quarantine island used especially during the smallpox epidemic as a place for ships carrying disease to unload ill passengers.
- "Spectacle Island Factsheet". Boston Harbor Islands Partnership. Archived from the original on October 5, 2006. Retrieved October 7, 2006.
- "Boston Harbor Islands Ferry Schedule" (PDF). National Park Service. Archived from the original (PDF) on July 26, 2007. Retrieved July 27, 2009.
- "Spectacle Island offers spectacular views of Boston Harbor". CNN.com. July 26, 2007. Archived from the original on August 6, 2007. Retrieved 2007-07-28.
- "Islands You Can Visit - Spectacle Island". Boston Harbor Islands Partnership. Archived from the original on October 5, 2006. Retrieved October 11, 2006.
- Klein, Christopher. Klein, Christopher (June 22, 2008). "A harbor Spectacle". Globe Newspaper Company. Retrieved June 6, 2009.
- Klein, Christopher. Discovering the Boston Harbor Islands: a guide to the city's hidden shores. Boston, MA: Union Park Press, 2008. Print.
- "Historic Light Station Information and Photography: Massachusetts". United States Coast Guard Historian's Office.
- "Broad Sound Channel Inner Range Lights: History". Jeremy D'Entremont.
- Sherman, Annie, "The Other Islands: The Harbor Islands make for an easy day trip for sunbathers, history buffs—and especially the traffic-weary" Archived 2008-05-06 at the Wayback Machine., Boston magazine, May 2007 issue.
- Forry, Ed, "Great Summer Get-a-way Just Off Our Coast", Dorchester Reporter, Editorial, July 12, 2007, p. 11.
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