The Samaria Gorge is the longest gorge in Europe — 16 km from the Omalos plateau down to the village of Agia Roumeli on the Libyan Sea — and one of the great walks in the Mediterranean. It descends through spectacular limestone scenery: narrow passages (the most famous is the Iron Gates, where the walls close to just three metres apart), clear streams, ancient plane trees, and the occasional Cretan ibex on the cliffs above.
The walk is downhill the whole way, taking 4–7 hours depending on pace. The gorge opens from May to October (exact dates vary); check before you go. Take the early bus from Hania to Omalos, walk down, and catch the ferry from Agia Roumeli to Hora Sfakion, then a bus back to Hania. The full circuit takes a full day. You cannot sleep in the gorge or spend the night in Agia Roumeli unless you book ahead — most people do it as a day trip from Hania or Rethimno. Bring water, good shoes, and snacks.