1) J.K. Rowling's "Harry Potter" series of books has sold over 500 million copies worldwide and has been translated into 80 languages.

2) The strongest natural material known to man is spider silk. It is stronger than steel and more flexible than nylon.

3) In Norse mythology, the World Tree, known as Yggdrasil, is a massive ash tree that connects the nine realms of existence. It is considered the center of the cosmos and serves as a conduit between different realms, including Asgard (realm of the gods), Midgard (realm of humans), and Helheim (realm of the dead).

4) The construction of the Great Wall of China began in the 7th century BC and was completed over several centuries, spanning thousands of miles.