This paper presents a first person outdoor/indoor augmented reality application ARQuake that we have developed. ARQuake is an extension of the desktop game Quake, and as such we are investigating how to convert a desktop first person application into an outdoor/indoor mobile augmented reality application. We present an architecture for a low cost, moderately accurate six degrees of freedom tracking system based on GPS, digital compass, and fiducial vision-based tracking. Usability issues such as monster selection, colour, input devices, and multi-person collaboration are discussed.