This paper introduces GLAM, a system based on situation calculus and meta-rules, which is able to provide adaptation by means of selection of actions. It is primarily designed to provide adaptive navigation. The different levels of conception, related to different aspects of the available metadata, are split in different layers in GLAM, in order to ease the conception of the adaptation system as well as to increase the potential use of complex adaptation mechanisms. GLAM uses meta-rules to handle these layers.