Dr. Dre's mega-mansion in L.A. is a sight to behold, but he's looking to add even more awesomeness to it ... underground.
According to L.A. City docs, obtained by TMZ ... Dre's got plans to dig up a huge portion of his property -- roughly the size of his home -- to build a basement (or bunker? or music studio?) featuring a few lightwells. He's also obtained permits to add retaining walls around his palace ... and a guard house.
It's unclear what the whole project's gonna cost the music mogul, but with excavation and additions -- along with construction of an underground fortress -- it could potentially be millions.
FYI -- Dre applied for the permits a few years ago, but he just got them granted this month.
Dr. Dre's mansion sits on 4 acres in Brentwood and features an infinity pool with ocean and canyon views, a poolside cabana, a gym, an outdoor kitchen and living area, 7 fireplaces ... and a freakin' moat.