Mark Wahlberg -- Building Huge Paris Mansion ...In L.A.

The only thing more awesome than the massive French manor Mark Wahlberg is building for himself ... is the WATER PARK-LOOKING THING he's creating in his backyard.

Wahlberg's mega-mansion -- which would look right at home in Paris (either France or Vegas) -- is under construction in Beverly Park ... a neighborhood that carries the exclusive 90210 zip code .... but is actually in L.A.

We're told .. .the house has all the amenities you'd expect -- home theater, wine cellar (natch), gymnasium and 2-story wood paneled library. When it's done ... the whole thing will cover 30,000 sq. feet.

Check out the pics ... and dig the the mountainous, rockscaped swimming pool in the back -- complete with waterfalls and a diving rock -- that's built right into the hillside.