According to Lynch (1960; p. 83) “the sequence [of landmarks] facilitates recognition and memorization”. Thus, under which circumstances do landmarks facilitate wayfinding? We therefore investigated the helpfulness of landmarks during route knowledge and survey knowledge retrieval from long-term memory. A field study with citizens of a street festival in a mid-size German town (Giessen) was performed. Sixty-three participants had to draw the shortest possible route between two given locations in the town. Within this experiment, two different conditions were tested respectively: drawing the route without landmarks and with additionally presented landmarks. A comparison of conditions revealed different performance groups: perfect performance (8%); performance improvement with additional landmarks (32%); equal performance in both conditions (36%); and performance decrement with additional landmarks (23%). These results were confirmed in two further experiments. We demonstrate that the decremental findings may be a result of the so-called visual impedance effect (Knauff & Johnson-Laird, 2002).