A bit late maybe, but being a newbie on this board I did a lot of reading.
For your Barcelona stay. This year is Gaudi Year, Gaudi was a pretty famous architect at the late 1800. His most prestige object in Barcelona is La Sagrada Familia, which is a must to see. This very huge and long time building Cathedral is so beautiful and is still under construction for over a 100 years now.
Gaudi himself is burried somewhere in or just outside the Cathedral, but no one tells you where ☺
Since there are festivities all around the city, you best can take the red hop-on-hop-off busses for both tours. There is a route north part and one for the south part of Barcelona. If you do this, you saw pretty much all of Barcelona.
If you are interested, there is a Hard Rock Cafe at the Plaza Catalunya, which is at the end of the Ramblas, for a nice lunch.
If you take a walk from the harbour to Plaza Catalunya over the Ramblas, mind that there is a fruit and vegetable market halfway on your left hand side, which is worth walking through.
If you have time enought in Barcelona, then go also to Parc Guell. Gaudi has lived there for many years and his influence in the Parc is obvious. If you like bright coloures mosaiques, you like the parc.
Just be sure you keep your money close to you, because pickpockets never sleep.
Since you go in October, bring a raincoat and something with long sleeves.
Keep track of the currency Euro against US dollar, today they have the same currency, so you can spend a Euro as you spend a dollar.
I wish you a good time in Europe!
Jacqueline from Amsterdam