The Buda hills consist mainly of limestone and dolomite, the water created speleothems, the most famous ones being the Pálvölgyi cave (total length ) and the Szemlőhegyi cave (total length ). The hills were formed in the Triassic Period. The highest point of the hills and of Budapest is János Hill, at above sea level. The lowest point is the line of the Danube which is above sea level. Budapest is also rich in green areas. Of the occupied by the city, is green area, park and forest. The forests of Buda hills are environmentally protected.