Alonzo8100 cames from Canada, where in Canada I got no Idea.

The grotto is what people do for there pools, like a cave with a smaller pool inside, if you have seen the playboy mansion the series they have a grotto attached to their pool. Or you can have a submerged bar or island with structure in the middle.

If I'm understanding correctly, he want to use he's garage, turn that into he's grotto.

Here are 3 pictures found on Google images.