Was ist der Schlossberg in Graz?

Why this is the correct answer

Rising 473 meters above the surrounding city, the Schlossberg is the dominant natural feature of central Graz and was historically the site of the city's defensive fortress. While the fortress was largely demolished by Napoleonic forces in 1809, the Clock Tower (Uhrturm), built in 1561, was preserved by the citizens, who paid a ransom to save it. Today the hill is a public park accessible by funicular, lift, and stairway, and the Uhrturm remains the most recognized symbol of Graz.