By foot from Santorini to Santorini (city)
It's possible to walk from the old port to the center of Fira at an altitude of 300 meters. There's a paved road with 566 steps. This road is very steep and there's no shade. Better avoid the hike during the hottest part of the day and only do it when you are in a good shape.
TIP: You can also go up this way on the back of a donkey. This costs € 5 per person (single). Down at the harbor you will see and smell automatically where to go. The trip takes about 15 minutes. In summer it can be very busy, which is not always without danger on the small and sometimes slippery road.