"No swimwear is Tinto brass Black Angel (2002) aka Senso 45 full movierequired for your evening with us," reads this restaurant's dress code.

Located at the southernmost point of Norway's craggy coast, Europe's first underwater restaurant has opened, fittingly dubbed Under. And it's not just a restaurant.

Designed by Norwegian firm Snøhetta, it's a 34-metre rectangular prism slightly submerged five metres under the sea. Seriously, it looks like a modernist shipwreck.

Right at the end of the monolith, sitting on the seabed, there's an 11-metre-wide, floor-to-ceiling window which allows its 35-40 diners to check out any underwater action.

According to the design team, the municipality of Lindesnes where the restaurant is located, is known for its intense, rapidly changing weather conditions — just imagine dining here during a storm.

Snøhetta founder and architect Kjetil Trædal Thorsen says the structure "challenges what determines a person’s physical placement in their environment."

"In this building, you may find yourself under water, over the seabed, between land and sea. This will offer you new perspectives and ways of seeing the world, both beyond and beneath the waterline."

The menu from Danish chef Nicolai Ellitsgaard from restaurant Måltid will use locally-caught, sustainable wildlife and ingredients from the surrounding area like sea arrow grass, sea rocket and salty sea kale. And it's not cheap, with the 18-course "immersion menu" sitting at NOK 2,250 ($266) per person, wine or juice pairing extra.

"Just on the other side of our iconic window — the ocean is bursting with fresh delicacies from the sea, so the journey from the kitchen to the plate is minimal," said Ellitsgaard.

But the restaurant isn't the only plan for the space — it'll also function as a marine research centre, welcoming researchers and marine biologists to utilise external cameras and measurement tools to study any species living around the restaurant.

It's not a fully fledged marine research powerhouse, but local analysis and species monitoring could be the key to the restaurant's sustainability.

According to the design team, the concrete structure will eventually adapt to its underwater environment as an artificial reef for limpets and kelp — the kitchen will even be able to harvest ingredients from the building itself.

It's this dual function that's possibly the best part of the project, designed to open up a sustainability-driven dialogue between the kitchen and marine research teams — when is the best time to responsibly harvest from the sea, and which species?

Plus, the teams will apparently collaborate to help attract fish to the dining room window, so you don't have to stare at an empty seabed during your dinner, and the researchers have species to study other than kelp.

Want to book a table? The nearest airport is Kjevik, Kristiansand, which is 85 kilometres (52 miles) from the restaurant. But its waiting list goes all the way to September, so good luck.

Of course, Under is not the world's only underwater restaurant, with the Maldives alone laying claim to the world's first all-glass underwater restaurant, and the world's first underwater club.

Perhaps we all want to be mermaids.