Naadam is the national holiday of Mongolia.
It gives rise to festivities each year on July 11th and 12th in Ulaanbaatar and in the rest of the country the following week.
The Naadam festival in Ulaanbaatar is the most famous and most prestigious one, but if you get a chance, try to see those held in the rest of the country, there are many fewer people and the atmosphere is much more friendly and authentic.
This promotional video about Tourism in Mongolia will give you a brief idea about tourism in Mongolia. You can visit /www.mongoliatrip.com/ to choose a tour of your interest.
