Glen Auldyn

Glen Auldyn is a narrow valley about long on the Isle of Man, with a river of the same name. This flows in a NNE direction and flows into the River Sulby not far from its estuary, near Ramsey. It is entirely within the parish of Lezayre. The lower one-third of the valley is inhabited and is partly followed by the B16 road. This section is overlooked by Sky Hill.
The middle section of the valley contains a ribbon of mature oak woodland.
The valley contains the small church of St Fingan.
In the valley is an underground reservoir with a capacity of around which supplies the north and east of the island.
In May 2025, Manx [Wildlife Trust] announced that they had purchased 455 hectares of land in the upper parts of Glen Auldyn, including the moorland to the west, to create a new nature reserve where temperate rainforest will be restored. This forms Manx Wildlife Trust's 32nd and largest Manx nature reserve.