The northern Island in the Outer Hebrides is relatively flat and has beautiful beaches on its west coast. In addition to unspoiled nature, one of the main attractions on the island is the stone circle at Callanish, one of the best megalithic monuments in Europe after Stonehenge. The exact purpose of the monument dating back to 2,000 BC is unknown, although theories abound. A burial chamber containing human remains was discovered in the 19th century. Another important site is Dun Carloway Broch, a massive fortified tower dating back to the Iron age.