Gorge of Sougia and Lissos

If you are fit enough, then this gorge is highly recommended. Start at Sougia, and walk towards the little harbor. Past the harbor you will find the entrance. Follow the yellow rocks all the way up through the gorge and nature until you reach the plateau. From there you take the stone steps all the way down to Lissos and it's abandoned ancient village.
After exploring the paradise that is Lissos, you can take a boat back to Sougia for only a few euros.
Bring enough water and food. You can fill your waterbottles with groundwater at Lissos(clean and tasty), but there is no bar or restaurant to get some food.

About halfway through the walk from Sougia to Lissos, you have some wonderful views.