"It’s practically illegal to go to Barcelona and not visit La Sagrada Família, Gaudí’s extraordinary temple dedicated to the Holy Family—also known as the world’s largest unfinished church. The illusive end date remains a mystery—local theorists speculate it will never be done in order to preserve its in-process cachet. Be sure to book a ticket ahead (dates are available three months out) so you can get inside and gawk at the vaults and rainbow stained glass. When you go, spring for the extra audio guide and a trip up to one of the two towers—the Nativity Façade is our favorite." - Gemma Askham
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