Zürich is situated at 408 m (1,339 ft) above sea level on the lower (northern) end of Lake Zürich (Zürichsee) about 30 kilometers (19 mi) north of the Alps, nestling between the wooded hills on the west and east side. The Old Town stretches on both sides of the Limmat, which flows from the lake, running northwards at first and then gradually turning into a curve to the west. The geographic (and historic) centre of the city is the Lindenhof, a small natural hill on the west bank of the Limmat, about 700 m (2,300 ft) north of where the river issues from Lake Zürich. Most of Zürich's sites are located within the area on either side of the Limmat, between the Main railway station and Lake Zürich. The churches and houses of the old town are clustered here, as are the most expensive shops along the famous Bahnhofstrasse. The Lindenhof in the old town is the historical site of the Roman castle, and the later Carolingian Imperial Palace.