Crete

Realistic — take the 06:15 bus, you're in shade for the steep half, and the 16km reads worse than it walks. The grim part is the ferry-and-bus return; book the Chora Sfakion taxi ahead and it's a good day.

Chania — better old town, better beaches (Falassarna, Elafonisi), and Knossos is a doable day trip east. Heraklion is where the museum is, not where the week is.