If you come to Mongolia in winter you should go to Terelj national park and travel by dogsledding on the ice of river and snowy area there. Friendly Khaski dogs will serve you there. It is only 65km away from Ulaanbaatar. There is guy named Tuvshee, he is running this business for ages, expierenced guy. The trip is not only dogsledding but it includes other extreme activities such as horsesledding,horseriding,moto tour, ice-climbing. I hope you push yourself into some extreme things and will have a lot of fun for one day.