A bear in search of food walks 10 kilometers to the south, then walks 10 km to the east and finally 10 km to the north. At that moment he realizes that he is back at the starting point.
What color is the bear?
The bear is white since the situation described occurs in the North Pole.
There are only two possibilities for a circuit like the one described to be closed:
1) Starting exactly from the North Pole. Advancing in any direction goes south. If you then walk exactly eastward, you travel along a parallel, staying at the same distance from the North Pole. The final 10 km to the north close the circuit.
2) Something similar could be done in the South Pole, but in Antarctica there are no bears ...