So basically after managing to take 2 days off my surgery rotation, I booked my flights to Barcelona for just 1 full day and 1morning (before my flight back). Is it really doable to see Barcelona in 1 day? The answer is yes!
Barcelona has a very fast and efficient metro system that connects the main points in the city together and takes around 10minutes to get around the city from the major sites. The main point i recommend booking your hotel is next to Placa de Catalunya. This square is in the main part of Barcelona, super central and easy to access.

From Airport to the city center.
This is super easy, just grab the airport bus Aerobus (A1) to Terminal 1 (T1) and one for the Aerobus (A2) to Terminal 2 (T2). The bus usually costs 5.90euro per ticket transfer to and from the airport and the last stop is usually Plaça de Catalunya with El Corte Ingles Store just infront of the bust stop.

Night bus from Barcelona airport to City center:
There are usually 3 night buses that serve the Airport and the city. the N16, N17, N18 buses. The N16 Bus usually is faster as some other buses might have a detour to reach the center. The total trip to the city center lasts 30minutes approximately. A ticket costs 2.40euros. you can but directly from the bus driver.
Where to stay in Barcelona?
The main location to stay at is Placa de Catalunya. This is the main square that is right next to Las Ramblas, El mercado de Barcelona, the Barcelona cathedral and very well connected via metro lines. Various hotels can easily be found around the city center of barcelona. I usually use booking.com to book my hotel.
The hotel I stayed at was Cituat Vella Barcelona. Excellent cheap hotel in the center of Barcelona with great coffee just near by (Cafe 365). Great comfort and they also have a Jacuzzi on the Top floor. :))
Main attractions in Barcelona.
What Can you Visit in Barcelona in 1 day ?
1. Parc Güell
Colorful, cheerful, and full of whimsy, this beautifully designed 17-hectare park is a designated UNESCO World Heritage Site. Created between 1900 and 1914, the Park Güell includes 12 acres of landscaped gardens featuring Surrealist architectural elements created by Antoni Gaudí and eight acres of pristine woodlands (pine forest and olive groves).
Splendid fountains, viaducts, grottoes, a colonnaded hall, winding staircases, and semi-closed conversation seats are scattered throughout the garden space. These creative structures are decorated in multicolored ceramic fragments.
There are picnic areas and a spectacular terrace that offers panoramic views of the city and the sea. Gaudí himself loved this area of the city (the Gràcia district), and his home was located here
2. Sagrada Familia
The Basílica de la Sagrada Família stands in the northern part of the city, dominating its surroundings with its 18 spindly towers soaring high above all the other buildings. One of Europe’s most unconventional churches, this amazing monument is designated as a UNESCO World Heritage Site.
The most important Catalan architect of modern times, Antoni Gaudí was commissioned in 1883 to design this Basilica as a neo-Gothic church. But instead of following the plans, he created a signature example of his famous surrealistic Art
3. Las Ramblas
Las Ramblas Is one of the main locations, tourists identify with in Barcelona, this voulevard is 1.2 kilometres long connecting Port Vell to Plaça de Catalunya. This street is one of the main streets in Barcelona where most of the action happens. This place is lined with cafes, ice cream shops, The market of Barcelona and great architecture the city has to offer.
Las Ramblas divides the main quarters in half with the Raval area and the Barri Gòtic area on either side of the street.
although its one of the great attractions of Barcelona its also a place to look out for pickpockets, as robberies are common place.
4. Placa de Espania
Placa de Espania is one of the great sites in Barcelona, It houses the old fighting ring which is now a commercial center (You can actually go up and get some magnificent views from the top for free) and the prominent two towers.
Here you can find the museum Museum Nacional d’ Art de Catalunya, which by its own right is stunning and provides great views of the main square and fountain infront.