In 1883, the St. Louis and San Francisco Railroad bored a 400-foot long tunnel through the solid rock of Sunset Hill. The tunnel was built to decrease the grade from Valley Park to Kirkwood. It was one of only three tunnels on Frisco lines in the early 1900s. It is 20 feet high and 12 feet wide with limestone block walls and a vaulted brick ceiling. By the early 1900s, the tunnel height limited the size of the freight trains. In 1922, the Frisco began a cut south of the tunnel in order to lay a double track. The tracks in the tunnel were then used as a siding until they were removed in 1929. In 1931, the tunnel entrances were bricked over to form a commercial mushroom growing operation, which lasted until World War II. In 1972, new owner Thomas Biggs proposed a restaurant to be built in the tunnel, but his plan was rejected by the City of Kirkwood.

Read about the Meramec Highlands History

From Historic Kirkwood Landmarks
Read more about landmarks in Kirkwood at
http://www.ci.kirkwood.mo.us/com-dev/LANDMARKS01.QXD3.PDF
Foto source: Kirkwood - a pictorial history. Pioneer Bank & Trust