Conceived by Samuel Newhouse (1853–1930), a New York entrepreneur, this $5 million tunnel served many mines and intersected numerous veins of ore with a 21,968-foot bore that ended in Eureka Gulch, just west of Central City in Gilpin County. The tunnel is 8 feet tall and wide and without shoring, as it is carved from solid rock. Two seven-ton Westinghouse electric locomotives moved three-ton ore cars until a serious accident closed the tunnel for good in 1943.

The Argo Mill at the Idaho Springs mouth of the Newhouse Tunnel opened in 1913. The seven-story, steel-frame mill with corrugated metal covering is terraced up the mountain-side along Clear Creek and surrounded by tailing dumps. It is open to tourists, as is the nearby Edgar Mine of the Colorado School of Mines.