One of the world’s leading centers for plant study, as well as a lovely place to take a stroll on a nice day, the Arboretum was established in 1872 and is administered by Harvard University. The 281-acre park setting was planned and designed in collaboration with Frederick Law Olmsted. (As a National Historic Landmark, it's one of the best preserved of Olmsted’s landscapes.) Open to the public, this living collection of thousands of trees, shrubs, and woody vines is recognized as one of the most comprehensive and best documented of its kind in the world. In normal times, free guided tours are available on designated days throughout the year—check ahead for details.