With a population of only 500,000, Luxembourg is one of the smallest countries in the world. But what it lacks in size, it makes up for in beauty. The Old Quarter/city center is a UNESCO World Heritage Site, perfect for walking and exploring. The Bock Cliff is known for having a series of underground passages, many of which can be walked through. Beautiful nature can be found in Berdorf, while sites of religious and historical significance include the Echternach Benedictine Abbey and the Notre Dame Cathedral.