Imagine 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. It’s a world heritage site, but it’s my home and has been for almost 40 years,” Viladomiu says of the luminous apartment where she raised her two daughters, both of them now architects.

“Obviously, I can’t take the rubbish out in my pyjamas because people take photos or ask me if I’m the woman who lives upstairs, like I’m a character. That’s part of my life. But I know it’s a privilege to live here.”

The apartment belonged to her husband, Fernando Amat, owner of the much-lamented designer store Vinçon, akin to the Conran store in London, which closed in 2015. Viladomiu moved in with Amat in 1988.

While Viladomiu won’t reveal what rent she pays, she has what is known as a renta antigua, a fixed-rent contract, with the right to live there until she and Amat (from whom she is separated) die, at which time the not-for-profit foundation that has managed the building since 2013 will assume ownership. Contracts of this nature stopped being given out in 1985, but an estimated 100,000 are still in existence across Spain.

“When I moved in there was plenty of life here, lots of neighbours,” Viladomiu says. “Around that time the building was acquired by the Caixa Catalunya bank, which bought out tenants with generous offers in order to refurbish the building. I don’t know why they never made us an offer. We joke that they wanted us to stay here as some sort of attraction, like Snowflake, Barcelona zoo’s famous albino gorilla.”

Caixa Catalunya ceased trading as a bank in 2010 and joined with two other failed savings banks to form the not-for-profit foundation that now manages La Pedrera. The rest of the building now consists of offices, while some of the space is used for cultural events such as concerts.

Casa Milà, popularly – and pejoratively – known as La Pedrera (the quarry) was commissioned by Pedro Milà and Rosario Segimon, who had inherited the vast fortune her father made in the Guatemalan coffee trade. Work on the building was completed in 1910 and, like many of Gaudí’s works, it was greeted with derision, partly because it resembled the rockface of a quarry.

The building has been a Unesco heritage site since 1984 and has passed through various hands. At the start of the Spanish civil war in 1936 the local Trotskyist and socialist parties installed themselves in the lower floors; while over the years La Pedrera has housed a bingo hall, estate agents, consulates and an Egyptian prince.

Viladomiu’s apartment is not only large but, like all of Gaudí’s buildings, it is also light, with sculpted, curvilinear walls and balconies whose ironwork evokes animal and marine forms.

After Gaudí’s death in 1926, Segimon scandalised the architectural world when she ripped out or covered up much of the original detail in her first-floor apartment, the most splendid in the building, and had it redecorated in the style of Louis XVI.

Surprisingly, Viladomiu says there are no rules about what changes she could make to the apartment, but adds that she wouldn’t dream of changing anything, not even the ancient brass light switches. Besides, she says, everything still works.

She interviewed numerous former tenants for what became a work of historical auto-fiction, now published in English as The Last Tenant.

“The book is auto-fiction, but everything in it about La Pedrera is real,” she says. “It began as a series of interviews with former tenants, but a journalist friend said: ‘You should tell the story in the first person, along with the story of your family.’”

In both the book and in real life, various famous people have passed through the apartment, among them the architect Zaha Hadid, former Barcelona mayor and Catalan president Pasqual Maragall and the fashion designer Jean Paul Gaultier.

“I met Gaultier downstairs by the lift,” she says. “I had my arms full of bags of oranges and he was looking at everything with great enthusiasm. He asked me if I lived here and I invited him up to take a look around. ‘You’ve made my day,’ he said. Later he sent me a bunch of roses.”

2026 marks the centenary of Gaudí’s death; while in June the pope will visit Barcelona to bless the newly completed Jesus Christ tower in Gaudí’s masterwork, the Sagrada Família. Meanwhile, Viladomiu remains a living reminder that most of what Gaudí built wasn’t designed for tourists, but for people to live in.