Every tourist (except those from non-visa countries) must be in possession of a full valid passport, entry and exit visa. You may take visa from Mongolian Embassy where you need two photos, valid passport and authorization from tour operators.

Visa for individual travelers:
General requirements for all types of Mongolian visas are:

Visas, except transit visas are issued by the embassy’s organization concerned. The normal time required for a visa to be processed is one week, for a transit visa 48 hours without any authorizations.