Underwater restaurants are often heavily romanticized. For many, the term evokes an eatery that's legitimately submerged under the sea, most often with a glitzy, glass-encased dining room that's one part submarine, one part Spago Beverly Hills. These sub-oceanic joints are ultra-exclusive and can be found in far-flung locales like the Maldives or Dubai.

And real-deal undersea restaurants like that really do exist. But when a dining establishment bills itself as being "underwater," it usually signals a restaurant-within-an-aquarium arrangement with California Pizza Kitchen-esque price points and the occasional mermaid show. More often than not, these types of underwater restaurants can be found hundreds of miles from large bodies of water or in not-so-exotic locales like Orlando.

Europe's first self-described underwater restaurant is truly in a league of its own.

Aerial view of Under, a proposed underwater restaurant on Norway's southern coast Half in, half out: Under is a bit of a misnomer as the slender, concrete-sheathed structure is only partially submerged beneath the North Sea. The restaurant's entrance is accessible via the shoreline. (Rendering: MIR/Snøhetta)

To be built in the municipality of Lindesnes on Norway's windswept southern coast, Under — a fitting name that's also a play on the Norwegian word for "wonder" — takes the form of a slender, rectangular structure that gently slides into the rugged sea, halfway in, halfway out, perched atop a massive boat ramp. Under has one big boxy toe in the water, testing it out but never fully committing.

Patrons access the structure through a wood-framed portal on the rugged Norwegian shoreline. As the building slopes down, it eventually becomes submerged, going deeper and deeper before ending in the formal dining room and its spectacular panoramic window, which faces straight into the depths at nearly 20 feet beneath the surface. It's here, right in front of the 35-foot-wide window, that you'll find the best seats in the house.

Guests also pass through a half-sunken champagne bar during their sloping descent to the dining room, a smart idea in the event that anyone finds being submersed under the North Sea in a concrete box a touch unnerving. (An offering of liquid courage never hurts.)

inside dining room at Under, a proposed underwater restaurant on the southern Norway coast A dining room with a view: With seating for nearly 100 guests, Under's dining room will be located at the bottom of the half-sunken concrete structure; a massive acrylic window looks out into the depths. (Rendering: MIR/Snøhetta)

"Like a sunken periscope, the restaurant's massive acrylic windows offer a view of the seabed as it changes throughout the seasons and varying weather conditions," writes architecture firm Snøhetta, which envisions diners enjoying the views from a smattering of small tables right up front as well as a pair of long communal tables. Headquartered in Oslo and New York City, the firm's best known works include the Lillehammer Art Museum, a revamped and pedestrianized Times Square and the pavilion at the National September 11 Memorial & Museum. One of the firm's most ambitious in-development projects, the Willamette Falls Riverwalk in Oregon City, Oregon, also revolves around water — and how the public perceives and experiences it — but without the submersion element.

"One of the benefits of this building is how it links nature and land, and how you can come safe from the land and in a very dramatic way go down through this concrete tube to the nature at sea level, and experience what normally is not experienced," lead project architect Rune Grasdal tells CNN.

View inside the dining room at Under, a proposed underwater restaurant on Norway's southern coast. Fish-eye's view: A look into Under's dining room from nearly 20 feet beneath the North Sea. The restaurant will employ materials, lighting and sound that attracts marine life to the structure. (Rendering: MIR/Snøhetta)

While ostensibly a restaurant (acclaimed Danish chef Nicolai Ellitsgaard Pedersen has been tapped to lead the kitchen), Snøhetta believes the stark, semi-aquatic building sheathed in a concrete shell will serve a more versatile purpose than that of a landmark dining destination. Without offering too much further detail, the firm explains that Under will pull double-duty as a "research center for marine life" that pays "tribute to the Norwegian coast and to Lindesnes — to the wild fauna of the sea and to the rocky coastline of Norway's southern tip." From the Snøhetta website:

Informational plaques will be mounted alongside the trail leading guests to the restaurant entrance at the water's edge. This informational path tells a story about marine biodiversity and the Norwegian coast, weaving the narrative of the site into the overall restaurant experience, and ends at a ramp up to the restaurant.

While partnerships with a local university or scientific organization have yet to be named, Snøhetta imagines that Under will become a regular haunt of "interdisciplinary research teams" who will use the restaurant (during off hours, presumably) as a hub for studying marine biology while also working to develop the most dramatic view possible for guests. Per Snøhetta, the in-house researchers will "help create optimize conditions on the seabed so that fish and shellfish can thrive in proximity to the restaurant."

Exterior view of Under, an underwater restaurant proposed for Norway's southern coast Sunken alien spacecraft? Barnacle-encrusted sea monster? Fine dining establishment with singular views? Under has 'been designed with sensitive consideration for its geographic context and aquatic neighbors.' (Rendering: MIR/Snøhetta)

Mollusks on the walls (and on the menu)

One specific type of shellfish will ideally thrive in very close proximity to Under. As Snøhetta explains, the building's thick concrete walls will double as a habitat for bivalves, specifically mussels:

The sleek, streamlined form of the building is encapsulated in a concrete shell with a coarse surface that invites mussels to cling on. Over time, as the mollusk community densifies, the submerged monolith will become an artificial mussel reef that functions dually to rinse the sea and naturally attract more marine life to its purified waters.

It's unclear if these mollusks and their friends will be prominently featured on chef Pedersen's menu, but it's a safe bet they will be considering Under's strong locavore leanings.

"With the restaurant placed in the middle of the food source, it is only natural that the focus is seafood. But also other local produce and what we can forage in the woods, in the garden under water and on the beach will be on the menu," reads a special Under website, also designed by Snøhetta.

It all sounds tasty, captivating and maybe a bit claustrophobia-inducing. But don't go looking for reservations quite yet. Under, which will "provide an under-water experience inspiring a sense of awe and delight, activating all the senses — both physical and intellectual," isn't due for completion until the first half of 2019. It's also worth noting that sleepy and scenic Lindesnes is at a remove from the touristy hustle and bustle of cities like Bergen and Oslo. The closest major city, Kristiansand, is over an hour's drive away.

Whatever the case, the Norwegian tourism authority is already touting this world-class dining destination in Lindesnes, where the current top tourist draw is mainland Norway's southernmost lighthouse.

"We'll attract tourists from all over the world. That is our goal. I hope and believe that this will be the start of a new age for the travel industry," says project founder Gaute Ubostad, who already operates a popular seaside hotel in the area. "One of our main criteria is that our guests will get to experience something unique in the sea."

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.