Mountain Mile is an approximate 1.3 Mile (2.09 km) section of a purpose-built graded road situated between the 27th Milestone and 29th Milestone road-side marker's on the Snaefell Mountain Course used for the Isle of Man TT Races on the A18 Mountain Road in the parish of Lezayre in the Isle of Man.
The Mountain Mile begins at the nearby Guthrie's Bridge at the 27th Milestone on the Snaefell Mountain Course and incorporates the former East Snaefell sheep-gate, East (Snaefell) Mountain Gate and the Mountain Box. The A18 Snaefell Mountain Road was developed in the mid-nineteenth century from a number of pre-existing roads and bridle paths.This included the building of a number of sheep-gates including the East Mountain Gate, the Beinn-y-Phott sheep-gate and Keppel Gate. The primary road A18 Mountain Road section from Keppel Gate to Park Lewellyn (North Barrule) is a product of the Disaforesting Commission of 1860 As this section of the A18 Mountain Road is purpose built, it reflects typical nineteenth highway and railway construction practices with many small scale cuttings, embankments, revetments and follows land contours with purpose built graded-sections. For the 1934 Isle of Man TT Races major alterations to the Mountain Course are carried out which includes the removal of the East Snaefell Mountain sheep-gate.