Randy Johnson -- Selling AZ Mansion ... Movie Theater. Gym. Waterslide.

The Big Unit's unloading his MASSIVE pad ... so, if you're in the market for a 12-bathroom mega-estate with a fully functioning MOVIE THEATER -- ya might wanna scrape up $25 MILLION!

Here are the stats on Randy Johnson's Paradise Valley mansion:

-- 25,000 square feet on 5 acres
-- 7 bedrooms, 12 baths
-- commercial-grade gym on the property
-- tennis court/ basketball court
-- trophy room
-- waterpark-style pool with waterslide
-- wine cellar
-- massive garage
-- secret garden area

... oh ... and also the GIGANTIC MOVIE THEATER WITH REAL WORKING TICKET BOOTH!!!!