Check Out the Ultima IV/V Map Explorer
This is a straightforward project; it’s an online version of the overland maps from Ultima 4 and Ultima 5, which you can quickly traverse in order to explore the length and breadth of the continent of Britannia. Simple key commands allow you to toggle between the maps for Ultima 4 and Ultima 5, and between Britannia and the Underworld.
(Hat tip: Slashing Dragon)