This paper presents ARCHEOGUIDE, a novel system offering augmented reality tours in archaeological sites. The system is based on wearable and mobile computers, networking technology and real-time computer graphics and 3D animation and visualization techniques. The user can participate tours adapted to his profile and automatically receive information based on his position and orientation as calculated by a hybrid technique making use of GPS, compass and image-based tracking. The user can interact with the device via multi-modal interaction techniques and request navigation and other information. ARCHEOGUIDE has been tested at the archaeological site of Olympia in Greece.