Early in the morning (just before the sunrise, e.g. 6 a.m.) this place is wonderful. It looks like from a fairy tale. The evaporating water and the fog are very beautiful on sunrise. I'm not sure that it is freely authorized to get there but it is a part of the Vitosha 100km ultramarathon and you get there after 30 km of walking/running :) Keep in mind that this is the coldest place in the marathon.