Am currently in Santorini (and have been for almost a week) and thought I'd share some observations/advice I wish I'd known...I hope it doesn't come across as negative, Santorini is beautiful but I also feel like I was labelled a 'money pinata' at the airport...I doubt we will visit again as we'll have done the island and apart from Akrotiri there just isn't anything else to do here that warrants a second trip and we also just don't click with the very touristy 'vibe' of the island.
1) Santorini is VERY expensive. I live in London so am not usually shocked by prices, but I am here - it doesn't help that there aren't many options when it comes to food. There is no large supermarket (the ones here are really quite small) and Carrefour is massivley overpriced (as is Lidl) and I was charged €6 our first day for a (small) loaf of bread, 2 cans of coke and a bottle of water in our local mini-mart! Food is very expensive - we are staying in a (not terribly well equipped, but beautiful and cheap) apartment in Imerovigli. The food options near us are terrible - in terms of price. The standard rate appears to be about €8-13 for a main (if you want fish then basically double that figure). Starters seem to be €5-6 - bread is always extra. Not every taverna/cafe has a price list outside (this is the most annoying thing about eating in Santorini) and very few offer a menu of the day. If you want cheaper you can always go to a gyros place but one look at the 'meat' revoving in front of a heater and I realised that I would be getting an infamous 'donner kebab'. The cheapest snack place we've found is a gyros place in Fira (€4 for a falafel pitta) - just before you hit the main square and almost behind the cathedral. We ate last night at Vanilia (it is open, contrary to another post) - lovely meal (although not particularly generous portions) but it should have been lovely for the price - €108 for two, and we had the cheapest bottle of wine (€24). For comparisons sake I should point out that I could eat at Gordon Ramsay in London for less than that (though maybe with glasses as opposed to a bottle of wine).
2) If you do a boat trip beware that : (a) you will need €2 per person once you reach the volcano (this was not mentioned by anyone before we arrived at the volcano); (b) take some water with you, again our guide told us this - on arrival at the volcano (surely better to advise BEFORE setting off??) - we did take water but could see that others hadn't...so just be prepared; (c) if you do the whole day trip like ours beware that you will stop for about 2 hours in Thirasia - this is so you can enjoy a meal at the harbour - I'm uncertain if this is shameless product placement or a genuine attempt to give the tourists a nice meal. The prices did seem refreshingly cheaper than on Santorini so that is a plus point. However, we had brought our own food and so ended up killing time - there isn't a great deal to Thirasia and the climb to the top isn't really worth it (in my opinion). No-one told us we would spend 2 hours there until we arrived...
3) Santorini is indeed beautiful and parts of it are picture-postcard perfect (esp when the sun is shining - we had a day of rain and wind earlier this week!). However there isn't masses to do - some wineries charge you for tastings (Santos) others don't (ArtSpace) - but in my opinion the wine isn't really that good (apologies to all - it may be organic and traditional but it is too sweet and just not to my taste). The ancient ruins at Akrotiri are still closed (we knew this before arriving) but there are some museums in Fira - charging about €4-5 entry. Other than that the only thing to do is eat and enjoy the view. I think a week here is too long if you prefer a more active holiday or want to do something besides eat and look at a pretty view. The beaches aren't that amazing either (although interesting because of the black/red sand)...but you can definitlety get better beaches. Also, there aren't many local arts and crafts - and those that there are, are (you guessed it) - VERY expensive!
4) Driving around the island is OK (and we aren't massivley confident drivers) - there are plenty of petrol stations but not all take credit cards - ask before you fill up! We found car hire to be cheaper by booking it through our accommodation.
Two days to go...off to see Oia (again) now.