Elin Nordegren -- The Mansion ADULTERY Built ... Is Almost Complete!

Elin Nordegren is thiiiis close to moving out of her substandard regular-sized mansion and into her North Palm Beach MEGA-MANSION ... 'cause the home Tiger's infidelity funded is almost finished.

New photos of the place show the property is in the final stages. It was reportedly scheduled to be completed in December, but by the looks of things it might be ahead of schedule.

Elin has been living in a $4.25 million pad across the street ever since she purchased the new property for $12 million back in 2012.

As TMZ previously reported, Elin knocked down the original home on the property so she could build her dream house ... a 21,000 square foot mega-home, complete with 9 bedrooms, a 600 sq. ft. theater, 1,182 sq. ft. kitchen and a 460 sq. ft. "ocean loft."

There’s also plenty of room for her two kids… the mansion comes with a 300-square-foot playroom and a 70 ft. by 40 ft. swimming pool with a 12-foot deep end.

And how does she have the money to fund such a gargantuan project? Simple ... she got $100 million in her divorce from Tiger Woods after learning he was bangin' every skank, skalliwag and skeezer he could get his paws on.