Built on reclaimed land, Monaco's new Mareterra district blends cutting-edge sustainability with scenic sea views, offering a fresh way to explore the principality.

It was just past noon in Mareterra, Monaco's newest neighbourhood, and a crowd swelled on the terrace outside Marlow, the principality's first British fine-dining restaurant. Nearby, office workers stretched out on wide steps by the water for their lunch break. Promenade Prince Jacques, the 800m pedestrian walkway that sweeps around the sea-facing perimeter of Mareterra, was busy with parents pushing strollers and joggers pounding the concrete pavement. I paused to soak up the view across the expanse of blue sea towards the leafy Roquebrune-Cap-Martin headland and Italy beyond. The area blended so seamlessly with the surrounding landscape that I struggled to remember how, six months ago, this was still an unfinished construction site – and that eight years ago, where I stood was the Mediterranean Sea.

This reclaimed district, a €2bn project unveiled in December 2024, is Monaco's latest answer to a question it has faced for more than 150 years: how do you expand when you've already run out of land?

I walked along the promenade and ducked through a door along the path, entering a dark, concrete antechamber. Another door led through to the hollowed interior of one of 18 caissons, the 10,000 ton, 26m-high chambers that sit side by side like giant Lego bricks on the seafloor to create the maritime infrastructure of the new neighbourhood.

In the dark, unlit space, it took a while for my eyes to catch up to what my ears immediately recognised: waves, crashing against a wall then flopping back onto the water's surface. I peered over a thick railing separating me from the drop into the sea below. The Mediterranean surged up as if reaching for my attention, while the reinforced concrete chamber remained silent and immobile as it soaked up the impact of the swell.

The top of the upper section of each caisson, which is known as the Jarlan chamber, is above the waterline to allow water to flow in and out through thin, vertical openings on the outward-facing side. The design has been engineered to act as a breakwater to absorb and disperse the energy of the waves.

"That means, even during 100-year storms, they won't rise too high nor submerge [Mareterra]," said Guy Thomas Levy-Soussan, the managing director of SAM L'Anse du Portier, the developers of Mareterra, as we stood in La Grotte Bleue, as this space is called, named after the Blue Grotto of Capri. "When the Sun shines through the openings in the Jarlan chamber in the morning, there's a slightly blue hue to the space," he said, explaining the choice of name.

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La Grotte Bleue doesn't sparkle under the weight of four walls adorned in pastel pink and lavender purple quartz like its Instagram-pretty neighbour a couple of doors down, a meditation room for quiet contemplationdesigned by Vietnamese artist Tia-Thủy Nguyễn. And I probably would feel a little uneasy being in the dark space alone. Yet it has quickly become one of the Mediterranean principality's most unusual, and least glossy, landmarks, attracting a steady flow of people like me, curious for a behind-the-scenes glimpse of the technical ingenuity involved in reclaiming land from the sea.

Land reclamation is nothing new in Monaco, the world's second-smallest country after the Vatican City, where 38,000 residents cram into a territory just more than 22sq km in size. While a high proportion of that figure are millionaires, they're still living in the most densely........

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