Glen Auldyn is a narrow valley about 6 kilometres (3.7 mi) long on the Isle of Man, with a river of the same name.
The lower one-third of the valley is inhabited and is partly followed by the B16 road.
The middle section of the valley contains a ribbon of mature oak woodland.
[1] The valley contains the small church of St Fingan.
[2] In the valley is an underground reservoir with a capacity of around 6,800 cubic metres (240,000 cu ft) which supplies the north and east of the island.