It is long and rises in the Colzium Springs at Millstone Rig of the Pentland Hills. It travels through Harperrig Reservoir, past the ruins of Cairns Castle, through Balerno, Currie, Juniper Green, Colinton, Slateford, Longstone, Saughton, Balgreen, Roseburn, West Coates and on to the nearest it gets to the Edinburgh city centre at the Dean Village, on the site of old watermills in a deep gorge. This ravine is dramatically spanned by the Dean Bridge, designed by Thomas Telford, which was built in 1832 for the road to Queensferry, and lies next to the New Town.