BARCELONA, Spain — One disadvantage of living in a famous home — even one closed to the public — is that tourists tend to appear when you least expect them.

That certainly has been true at Casa Vicens, a Unesco World Heritage site designed in the 1880s by the great Catalan architect Antoni Gaudí.

Otto Herrero, who has lived in the house since he was a teenager, laughed as he described finding tourists in the garden, and even in the living room. “It can be inconvenient, but I’ve got used to it,” said Mr. Herrero, a web designer and photographer. “If they are polite, I’ll sometimes show them round.”

The house is owned by four members of the Herrero Jover family, including Mr. Herrero’s father Ignacio, and is divided into four apartments, occupied by family members. But Armura Capital, the investment arm of the Andorran company MoraBanc, is in the late stages of buying the building. It says the structure, which it plans to turn into a museum, is a “unique and exclusive” investment opportunity for its clients.