Yuzhen Park, usually called South Park, is one of Sofia's easiest green breaks south of the centre. It has broad lawns, ponds, play areas, and open-air cafes, with Vitosha often visible beyond the trees.
It is not a formal garden or a major monument, but it is useful if you want to see Sofia at its most everyday. Come for a walk, a coffee, or a slower afternoon between the central sights and the residential southern districts.