Randy Johnson's Massive AZ Mansion Hits Auction Block, Previously $25 Mil

Randy Johnson's big unit is up for grabs -- a 25,000 sq. foot estate with a full gym, game room, bar, basketball court and WATERSLIDE -- and all ya gotta do is be the highest bidder.

As we previously reported, the ex-MLB superstar put the house on the market for $25 MIL back in 2014 ... but didn't find a buyer. He slashed it all the way down to $14.5 mil before finally deciding to put it on the auction block.

The place is insane ... it's located in Paradise Valley. Here are the highlights:

-- 7 bedrooms, 12 baths
-- Full tennis court/ basketball court
-- Trophy room
-- Game room with bar and pool table
-- Music instrument room
-- Sick pool with twisty waterslide
-- Wine cellar
-- Massive garage
-- Secret garden area
-- Movie theater with box office

There's more ... make sure to check out the pics. The auction, hosted by Concierge Auctions, starts on Jan. 29.

There's no starting bid ... but in order to get in on the action, ya gotta cough up a $100K deposit and proof of income.