The first open-air bio pool in Serbia was built on Rtanj in 2019. It is filled with the mineral-rich water from the natural spring, discovered in 14th century, and needs no pumps. The water is chlorine-free; instead, plants and algae which naturally filter and clean the water are planted in one section of the pool. From this mini-lake, filtered water flows over several small steps into the pool. The shape of the pool is inspired by the Serbian ramonda flower, while the nearby hotel is shaped like a pyramid, mimicking the shape of the mountain itself.