1) The Great Barrier Reef in Australia is the largest living structure on Earth and can be seen from space.

2) 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.

3) The world's first stock exchange was established in Amsterdam in 1602.

4) The concept of gravity was famously described by Sir Isaac Newton after an apple fell on his head.