Slovenia, a former part of Yugoslavia that escaped the conflict in the rest of the Balkans, is known as "the green treasure of Europe". It contains regions of karst limestone that form many spectacular caves and over 80 natural arches. One cluster of these arches can be found near the town of Postojna in a small nature reserve called Rakov Skocjan. The arch pictured above, called Veliki Naravni Most, appears deceptively small in the photo, but it has a span of about 60 feet and is about 120 feet deep. Photo by Ray Millar.