BARCELONA -- It has survived the death of its architect, a dearth of funding and the destruction of its prototypes during the Spanish civil war. Now the Cathedral of the Sagrada Familia, Antoni Gaudí's surreal, unfinished opus, faces a new threat: plans to bore a high-speed train tunnel within meters of its foundations.

"What would possess someone to build a tunnel like this next to the heaviest building in Barcelona, the most visited monument in Spain?" said Jordi Bonet, who leads a team of 20 architects working to complete the 125-year-old basilica.