Windemere

Description
Located on a mountainous island in the icy seas northeast of the Dry Lands, the fortress of Windemere was governed by the dark sorceress Elistaria and used as a stronghold for the Oppression of Lord Blackthorn. With no hewn paths through the treacherous mountains, access to the keep required the use of either a grapple to scale the peaks or powerful magic. Daemons guarded the dark castle, watching over the high-ranking members of the Oppression stationed within. The Avatar visited this dark place in Ultima V at the behest of the archmage Flain for the purpose of retrieving a Black Badge to facilitate the infiltration of Castle Blackthorn.

When the Underworld collapsed, the ensuing tremors caused the entire island to sink into the sea and the fortress disappeared beneath the waves forever.

Windemere in Lazarus
In the Lazarus version, Windemere was once the keep of a member of the Great Council which Elistaria now used to train dark mages for the Oppression. Beside the Daemons, Skeletons also guarded the keep.