Despite widespread knowledge that physical activity is a valuable mechanism for preventing many lifestyle diseases, data from the 2001 Behavioral Risk Factor Surveillance System indicate that less than half of the US population met activity recommendations established by the Centers for Disease Control and Prevention. To increase physical activity levels, community officials around the United States have identified public parks as a convenient, low-cost resource to enable active living. However, the amenities of the built park environment that best facilitate active park visits are unknown. The current article describes the relationship of micro-level environmental components and park visitors' physical activity. Using the System for Observing Play and Recreation in Communities, park visitation patterns are documented and described according to user demographics. Broadly, visitors who were observed in park environments, which contained playgrounds, sport courts, and paths, were significantly more active than visitors in settings without these features. Furthermore, six types of built features were able to explain 58% of the variance in observed activity intensity among park visitors. Findings suggest that built features that support physical activity across the life span (paths and courts in particular) may be considered by community leaders seeking relatively low-cost mechanisms to promote physical activity among residents.