Bordered by Serbia to the west and Macedonia and Greece to the south, southwestern Bulgaria is a predominantly mountainous region. More than 50% of its territory is covered by forests, much of it protected, and thus the region is very popular among hikers during the summer and skiers during the winter. Spread around its mountains are many medieval villages, monasteries and churches. The most famous of these churches is the Rila Monastery, which dates back to the tenth century and was added to the UNESCO list of World Heritage Sites in 1983. The city of Sofia, the capital of Bulgaria, is located in the north of the region, and this city includes Numerous archaeological and historical sites provide evidence of continued human occupation of the city for at least 9,000 years, leading many to believe that it is the second oldest city in Europe.