If you like vast infrastructures such as railroads, ships, airports, highways, etc., the classic OpenTTD of transportation and logistics tycoons has a lot to offer. Free and open source, OpenTTD offers a vast array of maps, mods, graphics packs, and more. With its recent release on Steam, some people are getting back into the game or discovering its greatness for the first time.

Me: I'm addicted to the huge map of Europe, it's 8192x8192, 8192^2. It's... It's very big. It's all of Europe, a little bit of North Africa, most of Turkey, most of Russia. It was made by tiram2sue, an OpenTTD player from Korea, and a friend of mine, and I love it. It's so big that you can't see the whole thing in one screenshot at max zoom. The map is optimized to work with JGRPP, a release of OpenTTD, and can be found at tt-forums.net.

Anyway, I'm off to set up a multiplayer server for OpenTTD. Those are the rules. It should only take a few thousand hours to fill this beast of a map. Of course, that's after spending 10 hours deciding on trainsets and graphics packs; OpenTTD is available on its official dedicated website and on Steam.