Maastricht is a town of culture and history. Every weekend, Maastricht welcomes tourists eager to visit one of the thousands of houses protected by the government because of their role in history. Maastricht is also known for the structures that have played an actual role in history. The Hoge Fronten is an old fortification that protected the town centuries ago. Onze-Lieve-Vrouw is a 17th century structure built in a classic Gothic architecture. But what really captures the imagination of the tourists is the Hill of St. Petersburg. Beneath the hill are caves with more than 20,000 entrances and exits.