The central mountain at the Disc's hub. It is a spire of grey stone and green ice and is roughly 10 miles high. Suffice it to say, from the very top you can see right to the rim, but due to the flatness of the disc, this can also be achieved from the tops of fairly tall hills.
Atop it sits Dunmanifestin, the home of the Discworld's Gods. The vast magical field earths itself constantly on this mountain, and at night it glows with cold fire, known as the Aurora Coriolis. This phenomenon is also attributed to the phoenix dancing. Both are true.