Traveling to Barcelona then to Greece

I think 3 days is severely short for Barcelona, especially if it's your first stop after an overnight flight. In that case you may be so sleep-deprived and jet lagged you're a zombie on Day 1. I never pre-pay for anything on Day 1, because I know it will be a waste of money for me. Perhaps you'll be luckier than I am and deal well with the transatlantic flight, but even so I don't think you'll have enough time for Barcelona.

The city has a bunch of sights that pretty much require pre-purchased timed tickets (if you wish to visit them) in order to avoid very long ticket lines and possible sell-outs. It's not easy for a first-time visitor to decide how much time to allow for each site in order to time the ticket purchases for the following sights. It's a great walking city: the Barri Gotic, the funky modernista architecture in the Eixample, Montjuic, etc. It would be a shame to have to run from one timed-entry sight to the next.

So I don't think you really have nine days left for Greece. Because of the need to fly or ferry to the islands, one doesn't travel around Greece very rapidly, and your time allowance is less than ideal if you want to see more than one island. What you're thinking about doing is going to have you on airplanes or ferries 6 or 7 times in 15 days, leaving you probably only 8 or 9 full, non-jetlagged days for sightseeing, plus some scattered hours on the days you make long-distance trips.

Does this trip have to be a combination of Barcelona and Greece? I don't think you have time for both unless you want to rush around for the entire trip. I'd also be a bit concerned about the return flight to Barcelona. If that flight gets canceled or severely delayed, you could miss your return flight home and have to buy a last-minute replacement ticket at exorbitant cost. If you really want to combine two such distant destinations on one trip, I'd suggest scheduling Greece early in the trip so you're not rushing back to Barcelona on your next-to-last day. But for me a better solution would be to postpone Greece.

It sounds like you've already bought a round-trip ticket to Barcelona. For itineraries like this it's better to try to get a multi-city ticket so you don't have to waste a day returning to your starting point for the flight home.

Thank you for your input. What we have decided to do is immediately fly from Barcelona to Athens, spend 5 days there, ( maybe 2 days there spend in Hydra) then go to Santorini for 4, fly back to Athens and catch plane to Barcelona and do Barcelona for 4 days on tail end of trip. We decided that on the day we arrive in Barcelona we will be tired anyway so why not just go on to Athens and spend the evening there and the next 4 days. By putting Barcelona at the end of trip we avoid having to return to Barcelona for one night from Athens to catch plane the next day to head home. The only exhausting part will be the traveling from US to Athens all in one (actually 2) days. But we decided we would be tired anyway. Thanks again, I appreciate your suggestions!

Instead of spending your initial jet-lagged days in busy Athens, see if you can find a direct (or connecting) flight to Santorini from Barcelona. That would be a much more pleasant way to begin this journey. There's nothing like waking up on a Greek island on the first day of your vacation.

I'd spend 3 nights on Santorini, then ferry to Naxos for 4 nights, then ferry or fly back to Athens for 3 nights. Then fly to Barcelona to complete your trip.

Thanks for your input. At this point we have booked everything and think it will be a very doable itinerary for us. When we arrive in Athens, it will be late afternoon. We will spend the first evening just going out to dinner, unwinding and to bed early and then the next day ready to begin 9 fabulous days in Athens, Hydra and Santorini, then on to Barcelona for 3. Can't wait! Again thank you for your input.

I would say you need at least 4 days in Barcelona to get a decent flavour. I suggest you give a lot of thought to what you really want to see and do. Prebook only your top priorities if necessary, allow time to enjoy and absorb, and you'll be planning your next visit before you leave. 9 days in Athens can be done with excursions to nearby islands like Hydra...or daytrips to Delfi archeological sites. Athens needs at least 3 days to see the basic attractions...considering where you stay, what do you want, what is your budget. You can chooce suitale places, time on them and have a enjoyfull trip...so give us more speifications. 4 days in Athens, and 3 days to 2 different islands will be ideal... Why not rent a car directly in Athens? I can fully recommend https://aktis.rent/en which I use also every time I need a rental car flying in to Athens. Enjoy.