Midwinter was the first open world game I ever played, and, frankly, one of the few I still absolutely love. Not only did the game feature a huge, snowy, 3D island to explore with the help of skis, buggies, hang-gliders and even cable cars, it also managed to effortlessly support a unique blend of adventure and strategy gameplay elements. I'm pretty sure it was the first game to allow for first person sniping too.
Anyway. The game's one of Microprose's gems, but you probably knew that already, so here's a lovely copy of Midwinter for the Amiga that's made itself available on eBay. It comes in its original box with manual, map, 3.5" disk and technical supplement. Seller ships worldwide.