A novel outdoor Virtual Reality (VR) concept called Open-World Virtual Reality (OWVR) is presented that combines precise GNSS positioning and a smartphone-grade inertial sensor to provide globally-referenced centimeter-and-degreeaccurate tracking of the VR headset. Unlike existing augmented and virtual reality systems, which perform camera-based inside-out headset tracking relative to a local reference frame (e.g., an ad-hoc frame fixed to a living room), OWVR’s globally-referenced tracking enables a novel VR experience in which the user’s outdoor exploration is robust to extremes in lighting conditions and local visual texture. This paper introduces the OWVR concept and presents a prototype OWVR system with two candidate sensor fusion architectures, one loosely and one tightly coupled. Comparative performance is evaluated in terms of tracking accuracy and availability of an integer-aperture-test-validated fixed tracking solution. For scenarios with degraded GNSS availability, which will be typical for outdoor VR, the tightly-coupled architecture is shown to offer a critical tracking robustness advantage.