I second the trail from Fira to Oia. Time it so that you can get to Oia by sunset!Here are a few amazing places to consider hiking while you visit Santorini:
- Trail from Fira to Oia
- Skaros Rock
- Oia to Amoudi Bay
I am sure there are many other places, but these are a few ideas for hiking in Santorini. Enjoy your trip!