Beijing’s International Train Booking Office (Mon–Fri 8.30am–noon & 1.30–5pm; t 010 6512 0507) is at the International Hotel, 9 Jianguomenwai Dajie ( see map). Here you can buy tickets to Moscow and Ulaan Baatar with the minimum of fuss. BTG Travel have a desk for Trans-Siberian tickets that charges about the same. You can also buy tickets at the Foreigners’ Ticket Booking Office in Beijing train station though they aren’t much good on visa advice. Out of season, few people make the journey (you may get a cabin to yourself), but in summer there may well not be a seat for weeks.
Getting visas for Russia and/or Mongolia in China can be tricky, since regulations change all the time; it’s always best (and, sometimes, essential) to organize them in your own country. If you want to apply in Beijing, check first whether it will be possible; you may need to show proof of inward and onward travel, and possibly hotel bookings and an official invitation too. See Beijing embassy websites and seat61.com for the latest advice. It’s a lot easier, but a lot more expensive, to book a tour; see agents and operators for a few recommended organizations.
Chinese train #3, which follows the Trans-Mongolian route, leaves every Wednesday from Beijing station and takes five-and-a-half days. A bunk in a 2nd-class cabin with four beds – which is perfectly comfortable – costs around US$690. Trains leave Moscow for Beijing every Tuesday, though in this direction you’ll likely have to buy tickets through an agency.
Russian train #19, which follows the Trans-Siberian route, leaves every Saturday from Beijing station and takes six days. A Mongolian train leaves for Ulaan Baatur every Tuesday and costs around US$200 for one bed in a four-bed berth.
See companies offering Trans-Siberian tours and packages (see Agents and operators); of course they’ll cost more than doing it yourself, but it’ll save a world of hassle.