Murmansk, Russia, is the largest city north of the Arctic Circle. The city receives no sunlight for several months out of the year, making it one of the most psychologically extreme environments on the planet. Residents of the city (about 470,000) walk along artificially lit streets that give the appearance of sunlight, undergo artificial sun treatments (much like tanning booths), and often suffer from the condition known as Polar Night Stress. Polar Night Stress symptoms include fatigue, depression, vision problems, and susceptibility to colds and flus.