Synonyms of 'impassable'
If you describe something such as a barrier or a forest as impenetrable, you mean that it is impossible or very difficult to get through.
The range forms an impenetrable barrier between Europe and Asia.
Thesaurus for impassable from the Collins English Thesaurus
If a road, path , or route is impassable , it is impossible to travel over because it is blocked or in bad condition.