The Berber village of 1,800 inhabitants on the edge of the Sahara Desert was built underground to provide shelter from the extreme heat of the area. The so-called "troglodyte" dwellings are distributed around open courtyards about 7 metres deep, from which natural light filters in and which serve as a collection system for the scarce rainwater. The site is also known for having been the set of George Lucas' Star Wars Episode IV.

The mining town of about 1,600 inhabitants located in a desert area in South Australia is also known as "the opal capital", as its mining sites provide the world's largest production of this mineral. What is special about the place is that the town's life (not only as concerns mining) takes place mainly underground, with houses, museums, art galleries, churches and shops, due to the prohibitive climatic conditions on the surface.

The Yaodong, traditional dwellings carved into the rock walls of the Loess Plateau in the northern province of Shanxi in China, have been inhabited for thousands of years due to the sandy and resistant soil that provides excellent thermal insulation and protection from the extreme weather conditions of the area. In some areas of the region these houses, embedded in the rock or distributed around open courtyards sunk into the ground through which light filters, are still inhabited.

The Sassi of Matera are an anthropic settlement developed starting from the Paleolithic which today includes the two neighborhoods of "Civita" and "Piano" in the historic center of Matera. Renaissance and Baroque facades overlooking 8th century cisterns converted into houses, underground dwellings (excavated until the 1950s), rock churches, vegetable gardens and hanging gardens describe the composite landscape of this stone city, declared a UNESCO heritage site in 1993.

The cavernous church, located in the Töölö district, is literally sunk into the rock, which envelops the circular room with rough exposed stone walls and from which water sometimes flows, creating small waterfalls. The only element emerging on the surface is the copper dome, arranged on a glass band which accentuates its "suspended" character. The building is known for its excellent acoustics.

Skinny exposed concrete volumes partially underground and embedded in the landscape like geological remains attacked by vegetation: this is how the five villas that were meant to literally disappear into the landscape of the Costa Smeralda were conceived. Out of five, only one was finished according to the original plan and the others heavily altered. The recent renovation, by Ferdinando Fagnola (the architect who originally designed the complex) and PAT. Architetti associati, has made it possible to recover three of the five villas according to the original spirit, through a new spatial organisation, new volumes and the technological retrofitting of the complex.

The house, formerly army barracks, is also known as "The Teletubbies House" because of its playful character and underground location which evoke the houses of the namesake BBC. The building is partially embedded in the hillside, to impact as little as possible on the listed landscape of the Pembrokeshire Coast National Park and is only revealed on the outside through the large living room window facing Druidston Haven and St Brides Bay. The simple, functional interior is animated by bright yellow color blocks, giving the space a lively, informal feel.

Clashing with the typical patterns of vernacular Alpine architecture, the holiday home near Peter Zumthor's thermal baths in Vals is set into the mountainside, from which it overlooks the valley through a large glazed opening describing an elliptical arc on the ground. Local materials and construction techniques, including the façade made of quartzite, deeply anchor the building in the earth and in the spirit of the place. The villa is thermally insulated and has a geothermal heat pump, radiant floors, heat exchanger, and uses only hydroelectric energy generated by the nearby reservoir.

The house, designed in honour of the Korean poet Yoon Dong-joo, is inspired by the ancestral relationship between nature and man, and by the biunivocal dialectic entangling earth and sky. The building consists of a 14 x 17 metre concrete box entirely carved in the ground. The interior spaces (kitchen, a studio, two bedrooms, bathrooms), located in the centre of the excavation, overlook two open spaces: a thin slit through which light filters, on the one hand, and a courtyard on which domestic life expands and from which the gaze is projected towards the sky, on the other.

The complex is part of the Messner Mountain Museum, a circuit of six museums (Firmiano, Juval, Ortles, Dolomites, Ripa and Corones) spread throughout the Alpine region and dedicated to the relationship between man and the mountain: the building, embedded in the mountain peak at 2,275 m a.s.l. and almost entirely underground, emerges on the outside with fluid and sculptural volumes in concrete and glass that seem to be a continuation of the granite rocks and offer spectacular viewpoints over the Dolomites.

BIG's intervention expands an impenetrable concrete bunker from World War II, transforming it into a cultural complex perfectly integrated with the listed landscape of Blåvand in western Denmark. The building, totally hidden in the landscape, consists of a single 2,800 square metre structure with four exhibition spaces excavated in the earth and marked on the surface by a series of cuts in the hillside that lead into the heart of the museum.

The house, dug into the rocky earth to protect against the island's strong winds and almost invisible except from the sea, is built on three levels in a trapezoidal plot, following an orthogonal grid that generates a dramatic alternation of solids and voids. The rough finishes in rock and cement, wood and metal emphasise the cavernous atmosphere of the rooms, tempered by the large windows facing the sea. Ventilation and natural lighting, high-performance glazing, a green roof and stone walls with high thermal inertia allow for an excellent level of energy efficiency and microclimatic well-being.

The partially hypogeal house is set against the hillside, from which it is overhung by a green roof with avocado trees: a landscaping and technologically effective solution that offers optimal interior conditions in an area affected by considerable temperature fluctuations. Inside, the volume unfolds as a large exposed concrete container with a functional and flexible layout. The living area gives access to a panoramic terrace and connects the various adjacent rooms; on the opposite side, a patio dug into the ground provides further access and a second source of natural light and ventilation.

Multiple swirls of prefabricated composite of local waste earth and 4,000 recycled plastic bottles mould the shells of this house in Tamil Nadu and wrap space, rock and vegetation into a compact amalgam. Inside, the room with reclaimed wood trim dissolves its cavernous character with zenithal light from the glass roof, from which the tree canopies filter. Outside, the spiral volutes of the structures emerging from the ground act as seating, creating a connection with the place.

The library, located in an area previously occupied by building debris and redeveloped, is distributed around a crack carved into the ground, embraced by various reading rooms, with different heights according to the slope of the land: the lower ones are only accessible to children while the circular reading room, marked by hgher ceilings, bordered by shelves that continue radially up to the top of the roof, encourages meditation and contemplation of the sky that filters through the central oculus.