Glen Span is one of two rustic arches that form the boundaries of the Ravine, the stream valley of the 40-acre North Woods. Glen Span arches over the stream, called the Loch, at its south end, with Huddlestone Arch at its north end. Both stone structures are slightly sunken into the Park’s landscape – a design technique meant to preserve the aesthetic of the wooded setting. A steep cascade falls over a rocky incline to its west.

Designed by Calvert Vaux and Jacob Wrey Mould, Glen Span was built in 1865. It originally featured wooden trestles, rock pier supports, and a wooden railing. The arch was reconstructed about 20 years later, with its wooden portions replaced with rustic light-gray gneiss rock. The arch is decorated with geometrically shaped stones and small hollowed grottos embedded in its underpass. The structure spans 16 feet wide and over 18 feet high, carrying the West Drive above while a narrow footpath runs under it along the water.