Maeshowe is a Neolithic chambered cairn and passage grave located in Mainland Orkney, Scotland. Built around 2800 BC, it's a massive tomb with a mound covering passages and chambers made of huge stone slabs. The central chamber is illuminated on the winter solstice, and its construction required a ton of effort - like, seriously, thousands of man-hours. Maeshowe is part of the "Heart of Neolithic Orkney" UNESCO World Heritage Site and is believed to have served as an observatory and ceremonial site rather than just a regular old tomb. Vikings even raided it in the 12th century, leaving behind some cool runic inscriptions.