For about 300 years, the Dutch dug up their own farmland and burned it to keep their houses warm. That whole lake is the hole they left behind. The skinny islands with houses on them are strips of land they saved on purpose, because you can't burn wet dirt and they needed somewhere to dry it. The dirt was peat. It's basically thousands of years of dead marsh plants squished into a thick, spongy layer, and once it dries out it burns a lot like weak coal. Holland was sitting on meters of the stuff. At first people just cut it out with shovels. By around 1530 they'd dug down so far they hit the water table, so they started fishing it out instead. A guy would stand at the edge of a trench with a net on a long pole and drag black sludge up from under the water. That sludge went onto a narrow strip of land left running alongside the trench. The Dutch call it a legakker. They'd spread the peat across it, stomp it flat, cut it into bricks, and let the sun and wind dry it out. Then it got loaded onto boats headed for Amsterdam and Utrecht. You can probably see where this is going. Every brick they sold made the trench a little wider. People kept wanting more fuel, so the trenches kept getting wider and deeper while the drying strips got thinner and thinner. Then a storm would roll through, wash one of the strips away, and two trenches would turn into one big pond. Keep that up for a few hundred years and you end up with the Loosdrecht lakes. The strips in these photos are just the ones that made it. And this was way bigger than one town. Back in 1978 a Dutch researcher named J.W. de Zeeuw made the case that the whole Dutch Golden Age ran on peat, the same way Britain ran on coal. Historians still argue about how far to push that idea. What nobody disputes is that Amsterdam's breweries, brick kilns and salt works burned peat, and so did most of the fireplaces in town. One Leiden dissertation went even further and argued peat mattered more to medieval Holland's economy than natural gas matters to the Netherlands today. Sometimes the digging got completely out of hand. Just west of Amsterdam, peat cutting plus storms grew a lake called the Haarlemmermeer from about 9,100 hectares to 16,850. In November 1836 a storm pushed its water across 4,000 hectares toward Amsterdam. A month later another one flooded 7,500 hectares in the direction of Leiden. The government finally had enough, brought in giant steam pumps, and drained roughly 800 million tons of water out of it by 1852. Then they put an airport on the bottom. Schiphol sits on that old lake floor about 11 feet below sea level, so if you've ever flown into Amsterdam, you landed at the bottom of a lake that people helped dig out for fuel. Nobody ever drained Loosdrecht, so the drying strips just sat there in the water for a few centuries until people started building homes and boat docks on them. So the only reason those houses have anything to stand on is that somebody 400 years ago needed a place to dry out his fuel.