Khustain Nuruu National Park, also known as Hustai National Park, is in the Tuv Aimag of Mongolia.
A beautiful nature preserve. Home to the Takhi (Przewalski's) Horse.
Mountain steppe.
Takhi Horse and other native steppe species.Related Wikipedia article: Przewalski's Horse
In winter it is very cold (-30°C) but May through October is pleasant.
It is 100 km west of Ulaanbaatar. You can arrange a tour or hire a car or microbus. Almost all paved road, so it could make a nice trip via bicycle.
About US$10 per person.
Hike, or with a jeep.
Takhi Horses
There are gers (yurts) available for rent and a dining hall.
You may not be able to camp in the park, but you can camp almost anywhere outside. The Tuul river is on the South side of the park.