In the physical world, decision making in common navigation strategies is based on a mental map which includes a mental representation of geometric features such as distances and directions between places. We propose that decision making in the web is also based on a mental map. Contrary to the physical world navigation, the mental map used for web navigation describes a part of the agent's epistemology of the world, hence consists of semantic relations between concepts and includes hardly any geometrical features. We focus on the navigation situation where the detailed web structure is unknown to the agent before the navigation, therefore the agent's decisions are completely based on his semantic mental map. We give a potential structure of the agent's mental map, simulated using WordNet, and simulate the agent's decision making process during the web navigation. The simulation of the strategies allows to assess existing web environments with regard to ease of navigability.