Sandra owned a unit in a building that is packed with celebs -- Sierra Towers in WeHo. The apartment has 2 bedrooms and 2.5 baths, so it's not huge ... which makes it even more impressive that she sold it for $4.4 million.

She bought the pad back in 2014 for $3.55 mil and did some renovations, so even though she didn't make a killing ... she still made out pretty well.

Here's the thing ... this building has a marquis address, with celebs like Courteney Cox, Elton John, Adam Sandler, Kelly Osbourne, Cher and others who have populated the building over the years.

Fun fact ... Lindsay Lohan once lived there and her pipes burst when she was in New York and it absolutely flooded the apartment below. Thing is ... the person who owned the building directly below her was Harry Morton -- Lindsay's ex!!!

Sandra's unit was on the 22nd floor, and it has a sweeping, jetliner view of L.A.... from downtown L.A. to the blue Pacific.