After having a hefty $5 million thrown at it, the previously run-down Hotel William, on Sydney's William Street, has reopened to re-reveal some majestic bones, a stunning rooftop and a modern Japanese menu.

Owner Warren Livingstone has also given it a new name, Hyde Park House.

There's a traditional public bar on the ground floor, and while Livingstone won't open the rooftop bar until next month, customers can test-drive the menu from chef Taichi Ito (Sake, Darlo Country Club) at the first-floor cocktail bar, Jessie's.

Think small plates, hangar steak and veg Japanese style and, when the rooftop opens, it'll include a raw bar.

"The rooftop will be called Slim's, after American photographer Slim Aarons, and I've pulled Will Dangar in to do the landscape design," Livingstone says.

Dangar (Bucket List, The London) describes it as a "tongue in cheek" interpretation of Aaron's luxe style: "It's all white, pastels and succulents."

The designer believes rooftops are Sydney's new frontier. "It's such a fantastic city to see from roof level, there'll be a lot more of them" he says.

Daily 10am-3am (upper levels close at midnight).

47-49 William Street, Sydney.