Irkutsk and Ulaanbaatar are connected by the Trans-Mongolian railway, but there are not many trains that travel on it.
The most popular and reliable train is the daily train 306. It departs Irkutsk in the evening and arrives to
Ulaanbaatar early in the morning after 2 nights of travel. This train does not have 1st class cabins, but it is possible
to book (min. 2 people required) the whole entire 2nd class cabin if you want space and privacy.
Train 306 Irkutsk - Ulaanbaatar (daily in high season)