The Black Cuillin, which are mainly composed of basalt and gabbro, include twelve Munros and provide some of the most dramatic and challenging mountain terrain in Scotland. The ascent of is one of the longest rock climbs in Britain and the Inaccessible Pinnacle is the only peak in Scotland that requires technical climbing skills to reach the summit. Nearby Sgùrr Alasdair, meanwhile, is the tallest mountain on any Scottish island. These hills make demands of the hill walker that exceed any others found in Scotland and a full traverse of the Cuillin ridge may take 15-20 hours. The Red Hills (Gaelic: ) to the east are also known as the Red Cuillin. They are mainly composed of granite that has weathered into more rounded hills with many long scree slopes on their flanks. The highest point of these hills is Glamaig, one of only two Corbetts on Skye.