Under, Europe's aptly-named first underwater restaurant has opened in Lindesnes on the southern tip of Norway.

There, marine delicacies are served five metres underwater, offering a unique panoramic view of ocean life through a 36-square-metre window dubbed the "sunken periscope" by its designers from the architectural company Snøhetta, known for its celebrated buildings such as the Oslo Opera and the 9/11 Memorial Pavilion in New York.

The 26-centimetre-thick plexiglass window is designed to withstand storms, and the entire structure, with its thick concrete walls, is built to resist pressure and shocks from the rugged sea conditions.

The 34-metre monolith serves up to 40 diners, five nights a week. Customers enter the restaurant onshore through a wood-panelled passage and descend down a long, oak staircase into a dimly lit dining room.

The restaurant is located on the southern tip of Norway, where the brackish waters from the east meet the salty waters from the Atlantic, resulting in a rich variety of local fish fauna, according to Trond Rafoss, a marine biologist involved in the project.

The very name of the restaurant is based on a clever play of words. In Norwegian, "Under" means "under" as in being submerged, but also "wonder".

"It is without a doubt the largest one in the world and the only one in Europe," restaurant owner Stig Ubostad told the news outlet The Local. "We've been through so many consultants I think it's safer than anything else," Ubostad assured.

The menu consists of 16 to 18 dishes, costs NOK 2,250 kroner ($256) per person and double that if wine is included. Nevertheless, Under is fully booked for the next six months.