I have made multiple visits to the five accessible Gaudí properties in Barcelona over the course of the last 15 years. They are all worth visiting. My personal ranking order is Sagrada Familia, Parque Güell, Casa Mila, Casa Batlló, Palacio Güell.

Only the Nativity façade and the crypt of Sagrada Familia are part of the WH designation, being the only components of the church largely completed during Gaudí's lifetime. You can actually admire the façade from the sidewalk of Carrer de la Marina. But the church is so unique and incomparable both in its exterior and its interior that no visit to Barcelona can be considered complete without stepping inside for an extended look.

Parque Güell dazzles with features such as the Hypostyle Room (aka "Hall of 100 columns" - there are only 86 of them, in fact) and the main terrace with mosaic-decorated benches above it. If you come here early in the morning, it is a prime spot for catching the sunrise over the city.

Casa Mila is a remarkable example of ingenuity in civic architecture, with no two walls anywhere in the building meeting at a straight angle. Its roof, with dozens of chimneys shaped as fantastic sentinels, is delightful and even otherworldly.

Casa Batlló is also brilliant but I would rate its interior a notch lower than that of Casa Mila. The fish-scales exterior may be its most striking feature.

Finally, Palacio Güell, the earlier of Gaudí's major works is decidedly less exuberant than the other buildings on the list. The interior, nonetheless, offers some impressive features, and the roof is a vibrant predecessor of the more expansive roof of Casa Mila's.

The sixth property in Barcelona, Casa Vicens, has opened its doors to the visitors for the first time in history in November 2017. I stopped by to admire its exterior in the past, and it will now be a prime target for visit on my next Barcelona stay.

The final location of this serial site is the crypt in Colonia Güell, 25 minutes by car from the city center, which I have not been able to work into my plans on any visit to Barcelona.

Starting at sunrise in Parque Güell, it might be possible to visit five of Gaudí locations in Barcelona in a single day, but it will require uncommon effort at planning and you may end up feeling rushed if you attempted that. All six of them in one day are possible only if you do not go inside one or two. Each of the properties requires close to two hours in order to fully appreciate. Advance online ticket purchase (for a specific time-slot) is highly recommended for all locations except the park, and is absolutely essential for getting into Sagrada Familia.