Raurimu Spiral, Railway spiral in Ruapehu District, New Zealand.

The Raurimu Spiral is a single-track railway line in the Ruapehu District that winds around a steep slope with two tunnels, a complete circle, and three hairpin bends. The structure climbs 139 meters (456 feet) through a carefully designed series of curves.

The problem was solved in 1898 by a surveyor working for Public Works Department engineer Robert Holmes, who proposed a line looping back on itself and spiralling with tunnels and bridges at a gradient of 1 in 52. It replaced a rejected plan by Browne and Turner requiring nine viaducts down the Piopiotea River. Holmes reportedly visualised the layout in his imagination, and no single spot shows the whole line.

The spiral shows how engineers solved a difficult problem with creativity instead of brute force. Visitors walking or riding through it can sense how much thought went into working with the landscape rather than against it.

The line is an active railway, so the track itself is not a walking route. A lookout with a raised viewing platform is reached from a turn-off east of State Highway 4 at Raurimu, and from there part of the layout can be seen. No single point shows the whole spiral, so combine the lookout with a train journey.

Surveyor R. W. Holmes worked for engineer Robert Holmes at the Public Works Department when he devised the spiral in 1898. By all accounts he visualised the whole layout in his imagination, and there is no single spot from which the complete line can be seen.