Simulation game recommendations? (preferably available somewhere for download, like Steam/Origin/etc.)

I seem to have far too much time these days, and I've played all my games to death already. I'm looking to pick up a good "simulation" type game so it can hopefully keep my occupied for a bit longer than other games.

It looks like flying simulators can be fun, but I haven't read anything too particularly great about any of them. Do any redditors know of any good simulation games?