The correct answer is Nadiža. Sava Dolinka first comes to the surface from underneath Ponca in the Tamar , then it disappears and comes out the second time at the Zelenci nature reserve. The trip to the Nadiža chute begins at the Tamar mountain hut and leads along a fairly steep path for almost 1 kilometre.
It only takes 20 minutes to get to the spring, but you must have appropriate footwear and be quite fit. Access to the spring itself is only allowed if you are equipped with a helmet.