Ulaanbaatar
Ulaanbaatar is Mongolia's capital city and has a population of slightly over two million people, or about sixty percent of the country's entire population. You'll likely to arrive in Ulaanbaatar either by train, coming from China or Russia, or by plane. Many people use Ulaanbaatar as a stop off while doing the Transsiberian Railway. The city is a great place to organize a tour of the surrounding countryside. It's also good to allow yourself a few days to recover from your tour, enjoy some of the great food options, and see some of the fascinating cultural sights around town.
As a tourist, you're likely to stay on or around Peace Avenue, which is the city's main street and passes through the center of the city. There's plenty of shopping along the street, as well as many restaurants, many of which offer western food and cater to tourists. You may enjoy a western style meal after several weeks in the Mongolian countryside. You'll find the tourist information office on the Suhbaatar square.
You main options for getting around Ulaanbaatar are by bus, taxi, or on foot. When you first arrive, particularly if you reach the city by train, a taxi is the best option. You'll likely be tired as most trains are overnight, and while you may believe you can walk to your hotel, you really can't. Take a taxi. Buses are convenient as well, particularly after you've had some time to orient yourself with the city.
If you have a few days in Ulaanbaatar there are some interesting sights worth visiting. Head to the Natural History Museum, which can be entertaining, and check out the Gandan Monastery, or Choijin Lama Monastery. Also make sure you see a cultural show, which is quite interesting with its music an a very impressive contortionist.
There are a small handful of hostels in Ulaanbaatar that are quite affordable. Most will arrange tours of the country for you, but do read reviews ahead of time. You'll find it challenging to find a mid range hotel, but there are some more high end, western chains hotels around town as well. During peak season you should definitely make reservations in advance.