We drove from Opatija, Croatia into Slovenia on Day 15th of our Balkans tour. On our way to Ljubljana we stopped to visit the Postojna Cave located in the southwestern part of the country. Carved by the Pitka River over the course of one million years, this karst cave system has four caves interconnected by the same underground river. The entire thing runs for nearly 15 miles (24,130 meters) and is one of the country's top tourism destinations. A small passenger train takes visitors to a one-mile section of the cave that has a well lit cement-paved trail.