It’s easy to walk around the main areas of Santorini (Fira, Oia, and Immerovigli). There are lots of paved stone streets through the mid towns, albeit hilly. The hiking path from Fira to Oia is also relatively well-maintained and probably the closest thing to a true trail. However, outside of Fira and Oia, you will need to take the bus or drive to other parts of the island like Akrotiri.