America's 20 most-visited National Monuments
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18. Governors Island National Monument, N.Y.( National Park Service )
In New York harbor just a few hundred yards from lower Manhattan, Governors Island served as a military base for 200 years and was home to the U.S. Army and Coast Guard. It was shuttered in 1996 and became a national monument in 2003. Today the island offers biking, tours of historic buildings and art exhibits and performances. The park is still under development.
Visitors in 2009: 325,840
More info: http://www.nps.gov/gois/index.htm