Many museums are part of a network in which membership in one museum gives you free admission to the others. So say a friend bought you a membership in the Fort Lauderdale Museum of Art. As long as that membership is current, it entitles you to admission to more than 500 art museums nationwide. Or if you're a member of Fairchild Tropical Botanic Garden, you can get in free to several hundred other gardens in the American Horticultural Society network.
There are caveats. Membership in an art museum probably won't get you into a science museum for free. The networks are usually limited to the same type of museum. Not every garden or museum participates in what is called a reciprocal admission program. It may not entitle guests to admission to special exhibits. Often, museums in the same region, typically within 90 miles of each other, do not honor each other's membership -- if you live that close, they want you to buy membership in each. But generally, this is a great deal for roadtrippers. Call ahead to see whether the museum you're visiting will honor your membership and whether there are restrictions.
Photos: Membership in Fairchild Tropical Botanic Garden, top and at right, will get you admitted free to other botanic gardens across the country.