Cruise lines have long competed over bigger ships and flashier amenities, but one company is now taking that rivalry to new heights — literally. MSC Cruises has unveiled plans for a sprawling open-air “theme park” at sea aboard its upcoming flagship, MSC World Asia, including an over-water swing ride that will send passengers soaring above the ocean, according to a company press release. The attraction, called “Cliffhanger,” is billed as Europe’s first over-water swing of its kind, suspended high above the ship’s deck with unobstructed views of the surrounding sea. It will be part of a larger outdoor zone known as “The Harbour,” designed as a central hub for open-air experiences and family activities, the company said. The Harbour is expected to feature a ropes course, waterslides and what MSC says will be the longest dry slide at sea, along with a playground and gathering spaces, according to the announcement.…