ONBOARD THE OASIS OF THE SEAS -- Royal Caribbean Cruises Ltd. Chairman Richard Fain said very succinctly what was behind this 220,000-ton, 5,400-passenger ship: "We wanted to do something game-changing."

Fain's words resonated here, onboard the world's largest cruise ship, which in many ways is indeed a cruise industry game-changer.

The most striking feature about the Oasis, and what gives it the neighborhoods that make it most unique, is its split superstructure.

This enables the ship to have outdoor areas built into the central spine of the ship's interior. The result is the Boardwalk and Central Park neighborhoods.

Royal Caribbean International CEO Adam Goldstein said that in the early stages of planning what was to become the Oasis, the planning team felt the ratio of indoor space to outdoor space on such a large ship with a traditional enclosed design was "wrong."

When the team realized that the width of the ship would allow them to open up its spine to the elements, Goldstein said, "we got excited."

"That changed the ratio of what was external to what was internal," he said. "It still allowed us to not only provide incredible options but better options than ever before."

Those additional options, he said, were the additional outside space that enabled people to be under the sky in more places, to dine al fresco and to transit the length of the ship in either the outdoor Central Park or the indoor Royal Promenade.

"This made us confident we were onto something special," Goldstein said.

Royal Caribbean executive vice president of maritime, Harri Kulovaara, is the self-described "father" of the split superstructure idea. He said the concept evolved from his time with Finnish ferry company Silja Line, when the line designed a vessel with an atrium in the middle of the ship.

That atrium idea became the Royal Promenade on Royal Caribbean's Voyager-class ships. On the Oasis, the Royal Promenade essentially became two levels: Central Park is the roof of the Promenade, and two huge skylights on the Park filter natural light to the Promenade below.

Kulovaara said that one of the most remarkable elements of the Oasis was the amount of natural light the ship has, even in its interior spaces.

"Ships usually have low ceilings, with decks stacked like pancakes and with no daylight inside," Kulovaara said. "Opening the ship from the top changes all of that."