Bill Gates was, for a very long time, the world's richest man. He's also one of the most accomplished people in the history of computer science; perhaps only Steve Jobs could even run him close in those stakes. These days he's donated an enormous amount of his wealth to charity, but he still keeps this beautiful $147.5m home in Medina, Washington.
As you can tell from the charity donations, Gates is a giving person. Within (and beneath his property) are servers, which provide internet access covering the entire Washington state. All the standard pieces of the modern mansion are here; the bowling alley and the boat outside, but it's the huge library which Gates is most proud of. Visitors to his home are given PIN devices which allow them to change the temperature, lights and music themes of the house to suit themselves. Like changing the screensaver on his Windows software!