Polar Nights in Scandinavia:
Polar Nights are an interesting experience for travelers. In northern Scandinavia, during the Polar Nights there is twilight at most (depending on the location). This can last 2-3 months. In northern Norway's Hammerfest (northern-most city of the world) the sun remains hidden for 1,500 hours. However, it is not as dire as it may sound - during the Polar Nights, the landscape is covered in snow, beautifully reflecting the light of the stars above. Twilight around noon usually gives enough light to read by. The time of the Polar Nights is the perfect time to watch the Northern Lights (Aurora Borealis)!
What Polar Nights are:
A Polar Night is 24 hours of darkness inside the polar circles. A popular misunderstanding is that the locations experiencing lots of Polar days (= Midnight Sun) also experience the most Polar Nights. Twilight makes this untrue.
The Scientific Explanation:
The length of the darkness varies from 20 hours at the Arctic Circle to 179 days at the Poles. Due to twilight, not all this time is actually Polar Night. Keep in mind that the time above the horizon at the poles is said to be 186 days. The asymmetry in numbers comes from the days with partial sun being counted as "daytime".
If You Have Problems:
The period of polar nights can be take it out of you - more so than other natural phenomena - and can trigger light depression in travelers not used to Polar Nights. Travelers with seasonal affective disorder (SAD) are particularly susceptible. If in doubt, consult a doctor before you travel, or obtain medical help at your destination. Tanning beds can help replenish the body's need for light. Polar Days (the Midnight Sun) affect people as well, but usually not as much as Polar Nights.