Northworld is a collection of three David Drake novels. Each takes place in the 'Northworld' - a set of eight interlinked planets, connected via an interdimensional soup called the 'Matrix'. Nils Hansen is a supercop for the Universal Consortium of Planets (or whatever). After previous attempts to figure out Northworld failed, Hansen is sent solo to see the sights.
In the course of all three books, Hansen explores the various aspects of the Northworld - including the lizard plane, the dinosaur plane, the plane filled with sentient computers and the plane populated solely by depressed fungus. Most of these explorations, however, are merely cursory.
The majority of Hansen's time in all three novels is spent in the Open Lands, a generic medieval world filled with by-the-book feudal types, waving around swords and doing their damndest to expand to the village next-door. The one twist is the introduction of power suits - incredibly high-tech battle armor (think Iron Man with a lightsaber). This adds a particularly lethal twist to the medieval shenanigans.