The roundhouse is built of coursed mine rock masonry in the shape of a semicircle with a turntable in the center. The original structure, built in 1888 to service locomotives for the Hecla and Torch Lake Railroad, ran approximately 170 degrees around the turntable, and had twelve train stalls ranging from 75 feet (23 m) deep on the south end and 90 feet (27 m) deep on the north. The structure is built of random mine rock with brick arches over the windows with a shed roof. Train bay doors are spanned with cast iron lintels.
A later addition from 1902 increased the circumferential span of the building by 55 degrees, adding five train bays. In 1907, three additions were made: a small shed and drying house, and a 75 feet (23 m) by 60 feet (18 m) machine shop. The machine shop was roofed by a low gable, and the eaves and construction matched that of the original structure. Finally, in 1928 an 80 feet (24 m) by 37 feet (11 m) storage area.