Have you had enough of chocolate yet? Every year, the Dutch buy about 22 million chocolate letters to celebrate Sinterklaas. So no mars bars, but an explosive amount of cocoa. Speaking of explosives, did you know that the largest volcano in our solar system is located on Mars? The Olympus Mons is about 25 kilometres high, 550 kilometres wide and has a diameter of about 624 kilometres. This volcano is more than twice as wide as the Netherlands!