National Institutes of Health

Occupying more than 300 acres, this premier biomedical research institution searches for the cures to Alzheimer's, AIDS, cancer, and some of America's most debilitating diseases. Its medical library is the world's largest, and houses more than 5 million books and journals; tours explore its holdings and provide suggestions on how to do research. The visitor's center offers films and a slide show, and the DeWitt Stetten, Jr. Museum hosts displays on medical research. In the summer, the complex has a free film festival for visitors. A must for those who are fascinated by medicine and the workings of the human body. All tours and visits must be arranged in advance.