Valve has kicked off a Steam Treasure Hunt which runs from now through December 20, offering new challenges every 48 hours to provide chances at winning free games, and concluding with three grand prizes of 100 games of the winners' choosing, which is in no danger of being overshadowed by the opportunity to unlock Team Fortress 2 hats along the way. This announcement has details on the first set of tasks, and while they state that their lawyers tell them to say "No purchase necessary," three of the four of these are game achievements, so they are also offering sales on the three games involved, with 33% savings on R.U.S.E., 40% off on Poker Night at the Inventory, and a 75% discount on Chime.