Mariah Carey: I'm Italian Neighbors with Clooney!

Mariah Carey is shacking up at Lake Como in Italy ... which means she can literally row over and ask George Clooney for a cup of sugar ... if she baked. Or rowed.

Mimi got hooked up with an 8 bed, 8 bath lakefront mansion by Airbnb ... where she'll stay during the Italian leg of her 'Sweet Sweet Fantasy' tour. We're told the area is already flooded with boat paps waiting to catch a glimpse.

The mansion -- named Villa Napoleon -- was built in the 18th century, and for $12k per night ... is packed with luxuries like 11 fountains, a greenhouse, private dock, children's playground, gardens, home theater, and a bell tower. Yes ... a 12th-century bell tower.