1) In Norse mythology, Valhalla is a majestic hall located in Asgard, the realm of the gods. It is the afterlife destination for brave warriors who die in battle, where they are greeted by the Valkyries and engage in feasting, drinking, and preparing for the final battle of Ragnarok.

2) The Great Wall of China is not visible from space without aid, contrary to popular belief.

3) Mountains are formed through various geological processes, including tectonic plate movements, volcanic activity, and erosion.

4) The longest-running TV show in history is "The Simpsons," which has been on the air since 1989 and has over 700 episodes.