Accommodations range from decent modern accommodations to abysmal modern accommodations to traditional gers (felt huts, stretched over a wooden frame—in all, a fabulous experience, but don't expect private baths or coed accommodations). Hotels fill quickly, so book accommodations well in advance. The best hotels in Ulaanbaatar are the Genghis Khan, the Bayan-Gol, the Ulaanbaatar and the smaller New Capital Hotel. Rooms are even more difficult to find outside of the capital—there are few resorts, and they are extremely small.
Always remember that you are in Mongolia—accommodations which locals may consider four- or five-star might only rank two stars in your book. Supplies of water, hot or cold, and electricity may be haphazard. Be prepared to go with the flow and accept it as part of the Mongolian experience. Anything odd that does happen will be considered hilarious when you tell your friends back home.