Gigantic White Flower . . .

I stopped my car yesterday on the way to the library in Madison to photograph this huge flower. It is much bigger than a dinner plate ~ round platter size at least! It must be a hibiscus but this puzzles me because it was planted in the ground. I am quite sure that it won't survive the cold New Jersey winters. The house was a 19th century Victorian and I did not see a greenhouse on the property. Maybe the owner cuts them back and overwinters the numerous plants somehow. Good for her. I am much too lazy to bother with anything that needs coddling.