"A lot of what we do is directly related to strong landscape situations,” says Kjetil Trædal Thorsen, a founding partner of Snøhetta. This is rather an understatement with respect to their latest completed project, the $8.1 million Under restaurant at Lindesnes, on Norway’s southern coast, which plunges 16½ feet beneath the waves, to allow diners to get up close and personal with marine life on the North Sea floor. Commissioned by hotelier brothers Stig and Gaute Ubostad (one of whom is a keen diver), Under was initially planned for a quayside site next to their Lindesnes Havhotell. But after Snøhetta came on board, it was moved to a nearby rocky bay to achieve the strongest possible connection to the ocean at its wildest.

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Driven by a swashbuckling entrepreneurial spirit, the Ubostads aim to compete with similar submerged restaurants in warmer spots like the Maldives and Dubai. Inaugurated in March, Under seats 40 people, with more accommodated at the midlevel bar, and it is already fully booked until October. In addition to fine dining, it offers marine biologists unprecedented observation conditions, pulling off a trick similar to Snøhetta’s wild-reindeer pavilion in Norway’s Dovrefjell National Park. To minimize impact on the seabed (no dredging and pumping), the architects and their engineers, Asplan Viak, devised a clever construction solution by building the main structure on a barge next to the hotel, sinking the barge to leave the restaurant floating in the water, then towing the structure to the site with a crane vessel, loading it with water-filled containers to submerge it, and finally bolting it down onto pre-prepared foundations. None of the technology used was new—much of it comes from the oil industry—but its novel combination here was highly ingenious.

Eight steel piles descend 52 feet to secure a concrete platform cast in the shape of the building’s footprint. Concrete was also the obvious material for the shell (especially since Under is intended as an artificial reef on which marine life will grow), while the tubular surface it presents to the waves is the ideal form for resisting external pressure (a solution Snøhetta had adopted for the fly tower of the Oslo Opera). A cutaway in the upper part of the structure, which rises 10 feet above the waterline, allows for a small outdoor walkway and entrance porch, as well as exposing some oak boards that also line portions of the interior, like the soft part of a razor clam protruding from its shell. Linking the restaurant to land, a galvanized-steel bridge carries power and fluid lines on its underside.

In comparison to the outlandish strangeness of the object from the outside, Under’s interior appears curiously, and perhaps a little disappointingly, familiar. After crossing the varnished-oak entrance porch and passing through the raw-oak entrance hall, descending into the main space feels like entering a movie theater. “We wanted to avoid all sense of anxiety in an underwater restaurant,” explains lead project architect Rune Grasdal, “so, wherever you are, you can orient yourself with respect to sea and sky.” Just as in a movie theater, the farther down you go, the closer you get to the screen—in this case a 35-foot-long, 11-foot-high, 10-inch-thick slab of transparent acrylic—while the walls and ceiling, again like a cinema, are upholstered with acoustic panels (there’s even a movie-theater galaxy of twinkly lights above your head). Issues of condensation and insulation made it impossible to leave the raw-concrete interior of the tube exposed, so the interior fabric panels cover gypsum sheathing, a 15-inch layer of mineral-wool insulation, a waterproof membrane, and a 4-inch air gap.

“It’s not every day you construct a building both over and under water,” says Snøhetta’s senior interior architect, Heidi Pettersvold Nygaard, “so the authorities insisted it must be as fire-resistant as an airport.” The upstairs oak cladding is thus 11 inches thick; the oiled-steel sheathing on the lower levels is pretty hefty too, while the acoustic panels are made from flame-retardant fabric woven with a color gradient that morphs from red to blue the deeper you go. Under is a total immersive experience for which Snøhetta designed almost everything, from the raw-oak chairs to the steel serving table. Though they played it safe on the inside—this board-formed concrete redoubt, reminiscent of the Nazi bunkers that still dot the Norwegian coast, would have been a perfect candidate for the kind of radical experimentation proposed by Claude Parent and Paul Virilio in the ’60s—there are some deft touches. A vertical window dramatizes your descent below the waves; the blue color at the lowest level prolongs the aqueous light inside; and the problem of internal nighttime reflection is solved by lights on the sea bed, which also attract marine life. The scientists are thrilled, and have already observed jellyfish species they’d never seen in these waters before. But there remains the troubling existential question of who exactly is looking at whom in this disconcerting reversal of roles, where the humans are in the “aquarium,” and the fish are out in the wild.