Although Takhti Tepa is far outside the national park, it is still managed by it and you need permission from the border police because of its proximity to the border.
Just before the border with Azerbaijan, far away from everything, in the middle of an undulating steppe landscape, there is ONE hill (from a distance it looks like any other) on which around fifty mud volcanoes bubble away. Some are larger (5m), others smaller (5cm), some are cone-shaped, others are puddles, others are constant "mud dispensers" whose mud runs down the hill. Yes, the mud is cold and no, it doesn't smell. Well worth seeing.