A source told The Sun newspaper: "George has really brought a bit of California to London.
"His private area is amazing and is better than most people's houses.
"Because he's such a big star he can request pretty much whatever he wants and he usually gets it. Scene builders can build anything on a film set - and that goes for facilities for the actors too. It's quite a sight."
As well as relaxing, George, 50, has also had a basketball court installed so he can get some regular exercise.
But it's not just George who's allowed in the private complex, his co-star Sandra Bullock and her 16-month-old son Louis are regular visitors.
The source added: "George lets Louis play on his decking and has a right laugh with him. He is big mates with Sandra, they've known each other for years."