Book excerpt: Immerse yourself in the stunning flora and fauna, trails, ruins and other wonders the Patapsco Valley State Park provides. Patapsco Valley State Park is nestled in four Maryland counties - Carroll, Baltimore, Howard, and Anne Arundel. From its humble beginnings in 1907 as a 43-acre forest reserve to its expansion to over 16,000 acres today, this hidden gem has become a refuge for wild animals and native vegetation and a retreat from suburban and city life. With its eight developed recreation areas and over 200 miles of trails, more than a million visitors annually explore this vast area rich with history. Visitors have discovered the park's National Historic Landmark, the Thomas Viaduct, which remains in use today with modern trains passing over the first multiple-arch stone railroad viaduct in the United States. Other marvels from the past include remains of 19th-century mills and mill towns, the Civilian Conservation Corps' Camp Tydings, and the popular and scenic swinging bridge. Visitors to the park today continue to experience the joy of the great outdoors like millions before them.