How to get to La Sagrada Família on a six-hour Barcelona layover

After Clara and I booked our recent trip to Rome, the airline changed our flight times and we ended up with a six-hour layover at the Barcelona airport on our way back. This airport is beautiful and calm and not a bad place to spend six hours if you want to get some work done*, but on this particular trip we wanted to make it into Barcelona proper to see at least one sight: Gaudí's masterpiece basilica, La Sagrada Família.

Our first leg landed at noon and our second was due to depart at about six pm, so we had almost exactly six hours to make it to and from the city center. The internet was not very helpful in telling us how to get there, so I'm sharing what we learned in hopes it will benefit someone else. What follows is how we spent our time, hour by hour:

12:00-12:30: Get off the plane and follow signs for public transit.
We were aiming for a bus, but found ourselves at the metro: this turned out to be a great discovery as the metro connection to the airport seems to be relatively new.

You'll need two Aeroport-metro tickets per traveller: one for the way there and one for the way back. As of this writing, each ticket costs €4.50.

12:30-1:30: Take the metro to the Sagrada Família stop.
To do this you can take the L9 Sud line all the way to Collblanc, where you ascend an infinite sequence of escalators to transfer to the L5. Take this line to the stop called Sagrada Família. We found it helpful to pass the time with games and snacks.

1:30-2:00: Eat lunch.
We got cheese, bread, fruit, nuts, and chocolate at a grocery store about a block from the Sagrada Família metro stop and ate it on a park bench. For two people for lunch it was about 10-15 euros, not bad and very speedy!

2:00-3:00: Bask in the amazing church.
You don't want to skimp on this step.

3:00-4:00: Return on the metro the way you came.
Take the L5 line to Collblanc, then transfer to the L9 Sud and go all the way to the terminal where you originally entered: For us it was Terminal 1, the last metro stop on the line. It's extra important to hold onto your metro ticket for the return trip, because you'll need to feed it into a machine both when you enter at Sagrada Família and when you leave at the airport.

4:00-6:00: Your two hours at the airport before departure.
Congratulations! You've made it there and back again.

What made this possible: We entered the basilica via the very short timed-ticket line by booking our tickets in advance. The tickets are for fifteen-minute entrance windows (we selected 2pm, so could enter anytime between 2:00 and 2:15), so we did some serious calculating trying to figure out the earliest time we could be reasonably confident of being there. Our flight was actually a half-hour late—we were supposed to have a 6.5-hour layover—so we're glad we included as much wiggle room in our estimate as we did.

*We know the Barcelona airport is so nice because our voyage to Rome had the same six-hour layover. Clara filmed one of her videos there in a spacious and nearly empty waiting area with amazing natural light, and I got a lot of work done on my applications.