The "First Route", from to , was opened on 11 March 1884. The principal contractor of the works was J.W. Wright & Co. The route ascended the escarpment around Greenmount Hill passing through Boya, Darlington, Glen Forrest, Mundaring and Sawyers Valley before turning north to Mount Helena, originally known as White's Mill then as Lion Mill. A significant delay in construction was experienced at a site that became popularly known as Devil's Terror - a location between Darlington and Glen Forrest. Clay was struck when a cutting was under construction followed by a subsurface spring. The resulting flooding turned the clay into a bottomless bog. The rail alignment had to be moved 100 metres south along the bed of Nyaania Creek, which was diverted into a specially constructed channel.