Human and animal studies imply that sleep is a critical period for consolidation of recent memories. Whereas the majority of researchers focussed on the procedural learning, the present human study concerns how storing of spatial information and episodic memory are linked to sleep stages. Two city mazes, a simple and a complex one, were created by means of a computer program. Local aspects of these mazes appeared as street scenes on a TV-screen. Our subjects sat in front of the screen and manoeuvered through the maze by the help of a three-button PC mouse. Thus, each subject took a 'mental walk' through an imaginary city. The task was to find various end-points and to find the way back to the starting point. Subjects of two experimental groups 'walked' through either the simple or complex city maze for eight hours. Afterwards the subjects slept in our laboratory, where their sleep stages could be measured polygraphically. Subjects who had explored the simple maze showed considerable alteration in sleep architecture. They remained significantly longer in sleep Stage 2 than subjects who had explored the complex maze. Moreover, with successful orientation in the simple maze sleep stages occurred aperiodically, whereas walking through the complex maze was associated with sleep stages in accordance with ultradian cycles, as observed in a control group. Compared to subjects of the control group who had experienced neither maze, the subjects of both experimental groups had significantly enhanced EEG sleep spindle activities. Alteration in temporal architecture of sleep and selective prolongation of sleep Stage 2 following spatial orientation point to a functional linkage between cognitive mapping of space and sleep Stage 2 with enhanced EEG spindle activity.