I magine that you live in an enormous, beautiful apartment designed by one of the world’s most admired architects in the most expensive street in Spain and for which you pay a derisory rent, with the right to live there until you die.

Meet the writer Ana Viladomiu, 70, the last tenant of Antoni Gaudí’s Casa Milà on the elegant Passeig de Gràcia in Barcelona. Viladomiu is in fact the last tenant in any of Gaudí’s buildings, unless you include the peregrine falcons that nest in the Sagrada Família.

So what’s it like being the sole occupant of a building that receives about a million visitors a year?

“I’m used to all the visitors.…