Katy bought the house in 2017. It's just under 6,000 square feet with 5 bedrooms and 6 bathrooms. It has the obligatory pool, a gym, a sauna and a cold plunge. It also has private hiking trails. And maybe most impressive ... a long-ass driveway -- we're told it's the best one in the neighborhood.

Speaking of neighbors, they include Penelope Cruz, Adele, Zoe Saldana, Jennifer Lawrence, Nicole Kidman and Ellen.

She bought the house for $18 million, so she'll make a few bucks.

As for where she and her fam are moving ... that's unclear, but she does have an estate in Montecito -- home of Oprah -- where she spends a lot of time with Orlando and Daisy.