Even if you don't have any interest in caves, a visit to the Škocjan Caves is still a must, just for its sheer size. Besides the usual collection of stalagmites and stalactites formations, it contains the largest known underground canyon which extends into several underground chambers. The largest, Martel's Chamber, measures 308 m in length and reaches up to 146 m above the underground flowing river, making it the largest chamber in Europe and one of the largest in the world. Unfortunately, this chamber is not included in any of the cave tours, but instead, you can descend along endless stairs and clinging footbridges into other big chambers like the Murmuring Cave (Šumeča jama) where the Reka River, which created the Škocjan Caves, flows at the bottom. Impressively, Reka River continues to flow underground for a total of thirty-four kilometres before it resurfaces near the Adriatic coast.