Saguaro National Park, Arizona

Saguaro National Park protects the iconic saguaro cactus in a forest 3.5 million strong, where individuals can live 200 years and reach 40 feet tall, making it the densest concentration of these sentinel-like plants on Earth. Split into two units around Tucson, it boasts the most accessible Sonoran Desert wilderness in the United States, with over 30% of its trails starting within a 15-minute drive of the city center. Despite drawing 1.2 million annual visitors, it remains less crowded than #6, which sees 60% fewer tourists yet offers comparable desert vistas. Its proximity to a major city ensures that any traveler can immerse themselves in this arid wonderland without sacrificing convenience.