Final changes to Barcelona Itinerary- next week! :-)

La Sagrada Familia and La Pedrera both need to be pre-booked. However, I would be reluctant to slap down the entry fees (I think La Pedrera, at least, is over 20 euros) so soon after my flight is due to land.

Google Maps estimates transit time to La Pedrera at 28 minutes if you use the bus and 41 minutes if you use the Metro. Both are highly dependent upon the precise timing--i.e., whether you just miss a bus or train departure. In your shoes I'd spring for a taxi (assuming Enric doesn't come along and say that traffic makes that inadvisable).

The walk from La Pedrera to La Sagrada Familia is about a mile. The direct path would have you walking along Carrer de Provenca and/or Carrer de Mallorca. Those are parallel streets. If you have time (and your proposed schedule would certainly allow it), you can see some of Passeig de Gracia before heading over to the church. The "Block of Discord" (including Casa Batllo) is three blocks down toward the port from La Pedrera (turn left when you exit La Pedrera). The side streets between Passeig de Gracia and La Sagrada Familia are attractive.

On such a short visit I would not attempt Parc Guell without pre-booking my entry. I don't think your chances of avoiding a significant line are very good. The park opens at 8:30, so the line will have had a chance to build up before you get there. I could be completely wrong, though; I was there in August. Perhaps Enric will find this thread and give us on-the-spot advice.

Oh no, I wouldn't worry too much about the traffic at noon on a normal Tuesday (well, if you had arrived say the following week you'd be screwed because traffic is going to be hell during the celebration of the Mobile World Congress, much like every year!). If I were you, Lena, I would simply take a taxi from the airport, given your location, it's going to be the easiest way, otherwise you'd have to transfer and take a second bus/metro/train to get to the hotel. It should take you say 30' or so -assuming normal traffic of course.

Then, just a few yards to the left of the hotel entrance, on the same sidewalk, you have a bus stop... catch either bus #6 or #7 or #34, they come every few minutes.. and then you have a stop merely a block from La Pedrera, at less than 100 yards. It shouldn't take you more than 20' give or take from the moment you board the bus, it's roughly 6 or 7 stops: http://bit.ly/2lNQE9M

I agree with Ann, better pre-book all the popular sites, and Park Güell is one of them. Again, as I mentioned in another post earlier, each site has a limited capacity regulated by Law. In the case of Park Güell is around 400 visitors every half an hour. Almost in front of La Pedrera, there's a building called Palau Robert (Passeig de Gràcia, 107) which has a Tourist Office inside, on the first floor. Maybe you can check there and see which is the availability of Park Güell at that precise moment, if it's available, get a ticket and then you can just take bus #24 just in front to the east gate of the park... easy peasy. Check here, click on the Bus tab and then tick #24 to see the route.

Btw, the TO insists in recommending going to the park by metro..., tell them you prefer to go by bus and ask them for directions, trust me, you'll thank me when you see you don't have to walk this after the metro to get to the park: http://static.panoramio.com/photos/original/64067070.jpg Can you see the red sign at the bottom? the metro stop is still a further 200 yards to the left from there, and then you have to walk all the way up to get to the entrance of the park, and yet some 300 yards more to get to the entrance of the Monumental area... all uphill! From the east gate is a mere 50 yards on a horizontal flat surface. If anything, going by bus from where you are takes a bit longer of course, say 15' more than going by metro, but it's worth (I think!)

Enjoy