at 13,676 km (8,498 mi) in length, featuring a vast number of  islands  (approximately 1,400, of which 227 are inhabited), including  Crete , the  Dodecanese , the  Cyclades , and the  Ionian Islands  among others. Eighty percent of Greece consists of mountains, of which  Mount Olympus  is the highest at 2,917 m (9,570 ft). 1821