Open dawn to dusk. Hemlock Gorge in Needham, Newton and Wellesley is a small 23-acre wild area along the banks of the Charles River. The park is dominated by the steep gorge, the river, its surrounding stands of Hemlock trees and Echo Bridge, a huge granite and brick structure that spans the river and gorge. When built in 1877 by the Boston Water Works, the bridge was the second largest masonry arch in the United States. And in 1982, it was designated a National Historic Landmark. Atop the bridge one is afforded spectacular views of the river and neighboring lands.