Hibernation sites and home ranges of marked snails were recorded in the field for several years. Each individual usually returned to the same relatively small hibernating area every year. Shifts between alternative hibernation areas sometimes occurred. Most of the observed non-returns can be explained by changes in spatial behaviour of the preceding season rather than disorientation. Observations and experiments show the existence of a detailed memory related to topographical features of the hibernating area and lasting for at least three years. The snails seem to orientate towards a goal area which has been memorized at the preparations for hibernation during previous years. Experiments seem to indicate the importance of chemical cues. A probably adaptive potential for very detailed memorizing of topographical cues allows for localization of hibernation areas less than 30 cm in radius, and even accurate returns to previous sites, although no traces of these are left. It seems that the supposedly primitive brain of gastropods like Helix has a capability for complex and long-term spatial memory similar to that of the vertebrate brain.