You'd think when you spend $60 million to build a massive Florida house it would stay above sea level ... but not so with Tiger Woods, who has a GIGANTIC hole in his dining room!

Sources connected with the repair of the Jupiter Island mansion tell TMZ, the hole is "massive" and the underlying problem is serious.

Tiger apparently noticed sagging in the dining room. Contractors have now opened up the floor, creating a big fat hole, trying to determine what's causing the problem. They think the pilings may have been improperly set. They also fear some may be missing.

So far the problem seems limited to the dining room, but they don't know for sure.

Tiger's had more than his share of ups and downs with holes over the last few years ... for sure.