Melenio cafe is a great place in the centre of Oia. It is on a little terrace and has the best views over Santorini. Very different to the rest of the restaurants/cafes in the village, very relaxed with amazing cakes and fresh juices.
Oia hostel is a great, clean and cheap place to stay (and Santorini certainly isn't cheap). It's very un-hostel like in a positive way and in an excellent location.
Ammoudi port is the best place for a swim in Oia; however the climb back up to the village is pure torture. It is a rocky cove with the clearest water I have ever seen, but space is limited so get there early.
Visiting vineyards is a must, especially as most have small restaurants attached.
Also, Atlantis Books is a rare find of a bookshop anywhere in the world. It is in Oia centre and must be visited, international literature, and the shop is a delight.
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