The eye-level concrete slab slicing the sightline down a short lane at the end of the Žižkov number 9 tram is a surprise, even if you’re looking for it. But with EggO, a 2,300-square-foot, single-level home built by Prague architects A69, the surprises aren’t limited to the exterior.

EggO sits low on the street corner next to a row of prewar red-shingled houses. Its signature feature is a six-and-a-half- to eight-and-a-half-inch white concrete slab that stays straight and level even as the street slopes away. What isn’t apparent until entering the home and walking a few steps past the garage is that a large oval hole has been cut out of the concrete to frame an inner garden. Instead of landscaping around the house, A69 built the house around the landscape.

“My husband Tomáš used to live here with his parents in the old house next door,” says 38-year-old Johana Růžičková. Smiling and relaxing at the broad dining table, she adds: “Right here was his childhood place. It was just a garden, full of trees; it was a tree alley. These ugly buildings were not here.”

Johana is referring to the scene across the street, a long wall of what Germans call plattenbau: shoebox-shaped concrete prefab housing estates, rising eight stories and looming over the entire block. In Berlin, Leipzig, or Moscow, there’s an argument to be made for the much-maligned plattenbau, but it probably won’t go very far at this table. When Tomáš Růžičká returned to his childhood home as an adult and took in the altered surroundings, he figured he would never live here again; a house underneath this brutal block of concrete would feel too public, as if 400 pairs of eyes were looking right at him.

A ruddy, vigorous man with a clean-shaven head, Tomáš, 40, is straightforward about the difficulties involved. “I’m an engineer: heating, air-conditioning, electricity. That’s my advantage. But it was horrible to start my own house,” he says, laughing. “My friend Stanislav Fiala is also an architect. He said, ‘You’ll have trees there. It’ll be perfect.’ For me it was the first step. My way is to believe the architects.”

And so Tomáš turned to A69, a firm led by three architects all born in the same tumultuous year of 1969. The architects decided to meet concrete with concrete: pouring 1,765 cubic feet of concrete in situ to form a singular roof slab weighing 120 metrictons. “How to live in this garden,” explains 38-year-old architect Jaroslav Wertig. “How to use the garden without being dominated by the buildings across the street. That was the complication. So we created this opening in the roof. It originally should have been a circle, but when we followed the trees that were here already, it became ovoid.” The egg-shaped opening (which gave the house its name) also works to define an expanded sense of personal space, he notes, highlighting and focusing attention on the yard with its spruce and apple trees reaching through to the sky.

EggO is about where concrete is, and where it isn’t. A third of the oval’s diameter gives shape to a curved interior glass wall; the glass is attached to slender steel columns using the same technique automakers use to seal windshields onto car frames. These windows frame the main living space, gazing out onto the lawn and trees. The other side of the living room features a false wall surrounding a fireplace, above which rectangular windows let eastern sunlight into the room.

Those steels columns also bear the load of the concrete roof, with huge girders stationed in the garage. The girders are hidden from view by a checkerboard wall of steel baskets displaying rocks, bricks, and chunks of concrete saved from the construction site held in place with wire gabions (a detail Wertig says was inspired by Herzog & de Meuron’s Dominus winery in Napa Valley).

Another, thinner slab extends from the back of EggO to abut Tomáš’s boyhood home. It is covered with grass, creating an elevated garden accessible from the second floor of the old house, where Tomáš keeps his office. But this detail was also for his 92-year-old grandmother, Vera, who can now get fresh air without having to head downstairs or even leave the house. After all, the spaces of the house are not clearly delineated. Walking from the patio to the living room, or from the kitchen into the garden, doesn’t feel like going in or out—it feels like moving from a glass room into a green room.

As open as the house is, it was important that the interior could be partitioned. Because both Tomáš and Johana work from home, the entryway seals off to provide a place for the couple to meet clients.

In the end, the house is driven by insularity, closing out the city instead of embracing it—a paradox not uncommon to Prague: Many residents desperately want to get out of the city while at the same time loving it. But the Žižkov district and A69 may represent a broader city shakeup.

“I met the local planner at a party,” Wertig says, “and I asked him: ‘If I came to you two years ago with this project, would I get permission?’ And he said, ‘No, of course not!’” The planner may have been kidding, but Žižkov, once working-class, residential, and plain, is changing. It’s now home to bars androck clubs, and a new metro connection is on the way. But with a hearty stock of Art Deco and classical buildings downtown, new architecture in Prague is uncommon—and local attitudes toward new buildings reflect that. There is also latent public resentment at not having had a voice in urban matters under communism.

“I’m used to that antique style and always thought I would live like that,” Johana explains. She never thought she would want to live in something contemporary. “I know that conflict. I needed time to change the old things in my mind. I like this space. It’s so free.”

As the house grows up, the trees will form a leafy wall, with vines growing over the wire baskets and gabions. Which means that EggO has saved its biggest surprise for last: 120 metric tons of concrete will vanish into green, weightless, fully camouflaged from its surroundings.

Click here to listen to an audio interview with A69 Architects.