Skiddaw is a mountain in the Lake District National Park in England. With a summit at 931 m (3,054 ft) above sea level it is the fourth highest mountain in England. It lies just north of the town of Keswick, Cumbria, and dominates the skyline in this part of the northern lakes. It is the simplest of the Lake District mountains of this height to ascend (as there is a well-trodden tourist track from a car park to the north-east of Keswick, near the summit of Latrigg) and, as such, many walking guides recommend it to the occasional walker wishing to climb a mountain. This is the first summit of the fell running challenge known as the Bob Graham Round when undertaken in a clockwise direction.
The mountain lends its name to the surrounding areas of "Skiddaw Forest", and "Back o' Skidda'" and to the isolated "Skiddaw House", situated to the east, formerly a shooting lodge and subsequently a youth hostel. The name may be of Cumbric origin. It also provides the name for the slate derived from that region: Skiddaw Slate. Tuned percussion musical instruments or lithophones exist which are made from the slate, such as the musical stones of Skiddaw held at Keswick Museum and Art Gallery.
The bedrock of Skiddaw, commonly known as Skiddaw Slate, is the Kirkstile Formation. This Ordovician rock is composed of laminated mudstone and siltstone with greywacke sandstone. At the summit this is overlain by scree and to the south are areas where the underlying Loweswater Formation surfaces.