1/24 Underground ​Villa Vals, Valsertal Valley, Swiss Alps The surreal, hobbit-style Villa Vals is found in the unspoiled Valsertal valley of the Swiss Alps. villavals.ch

2/24 Underground ​Villa Vals, Valsertal Valley, Swiss Alps The stone house is completely dug out of the mountainside, with room for ten people to stay. villavals.ch

3/24 Underground ​Villa Vals, Valsertal Valley, Swiss Alps The views across the mountains from a huge glass facade opening out on to the terrace are unbeatable, as you might expect from a height of 1250 metres, and it is right next to peaceful ski slopes and Peter Zumther's famous Thermes Val hotel and spa. villavals.ch

4/24 Underground ​Villa Vals, Valsertal Valley, Swiss Alps Inside, the decor is fresh and contemporary and there is a long table for entertaining admiring guests. villavals.ch

5/24 Mountain ​Tucson Mountain Retreat, Arizona The Tucson Mountain Retreat in the Arizona desert is home to San Diego doctors David and Karen, who wanted to build a property that made little impact on the fragile environment but would keep them safe from extreme weather conditions. Bill Timmerman

6/24 Mountain ​Tucson Mountain Retreat, Arizona The house is reached by a narrow footpath that winds through a dense area of cacti and the steps are a fun sequence of concrete cubes. The layout is organised into three different 'zones' for living, sleeping and home entertainment. There are no corridors between these, so you must go outside to reach each one. Bill Timmerman

7/24 Mountain ​Tucson Mountain Retreat, Arizona The house is one-storey high with walls of rammed earth that absorb heat in the day and release it at night to minimise energy costs. Bill Timmerman

8/24 Mountain ​Tucson Mountain Retreat, Arizona Large glass doors erode the boundary between home and desert, with the sleeping and living areas extending into patios with views across the Sonoran Desert. Bill Timmerman

9/24 Mountain ​Tucson Mountain Retreat, Arizona The house has yet more eco credentials. It can store 30,000 gallons of rainwater collected on the roof, which is then filtered and used for the household appliances. Bill Timmerman

10/24 Mountain ​747 Wing House, California The 747 Wing House in California’s Santa Monica Mountains is made with the wings and tail fins of a jumbo jet. It was designed by architect David Hertz, who came up with the audacious idea during, you guessed it, a flight. The plane cost just £21,600, but the real expense came when the various parts had to be brought to the remote site by helicopter. The owner admits that the final bill came to ‘millions and millions of dollars’, but the ‘phenomenal environment’ makes it a price well worth paying - if you can. Rex Features

11/24 Mountain ​747 Wing House, California The plane’s wing forms the roof (strong enough to host drinks parties on), the fuselage and windows made a unique room divider and the front engine cover has become a fountain pool in the garden. The nose cone and cockpit were made into a ‘meditation pavilion’ on the 55-acre site, while remaining fuselage built a barn and caretaker’s house. Only the mid-section where the landing gear is stored has not been used. Rex Features

12/24 Mountain ​747 Wing House, California Hertz is ‘happy with the project in its entirety’ and it is now owned by a retired car dealer who owns Mercedes-Benz dealerships in the state, called Francie. Rex Features

13/24 Forest The Tower House, New York The Tower House in Upstate, New York was designed as a sustainable ‘stairway to the treetops’. There are tiny ensuite bedroom suites on each of the first three floors while the elevated living space sprawls along the top floor in line with the forest canopy, offering fantastic views of the lake and mountains. The outdoor roof terrace extends above the treetops and the glass-enclosed stairs highlight the climb to the skies and reflect the surrounding woodland abs camouflages it. Tiny lights dotting the stair rail mimic fireflies at night. BBC/Wall to Wall/Jack Dwyer

14/24 Mountain Te Kaitaka, Wanaka, New Zealand Te Kaitaka is inspired by origami, with folded angled roofs hiding skylights that fill it with natural light. Architects Gary Lawson and Nicholas Stevens wanted to architecturalise the triangle-shaped mountains and a landscape they saw as ‘fabric draped over rocks’. Horizontal and vertical lines have been abandoned to blend the house into the hillside so well that it is almost invisible from a distance. BBC/Wall to Wall/Jack Dwyer

15/24 Mountain Te Kaitaka, Wanaka, New Zealand The cedar-clad home, which translates to The Cloak, overlooks the glassy Lake Wanaka in the lush south island. BBC/Wall to Wall/Jack Dwyer

16/24 Underground ​Netherlands This solar-powered Netherlands home covered in earth is a sustainable dream come true. Keen for it to coexist harmoniously with the surrounding snowy hills, architects Denieuwegeneratie made an artificial mountain to bury it in. This innovative design means that the house is well-insulated, keeping energy consumption low. In fact, it produces more than it uses. Inside, there are spacious living areas that contrast with more cave-like rooms and corridors. The bedrooms are quirky and there are slits in the mountain for natural lighting. BBC/Wall to Wall/Charlotte Lee

17/24 Forest ​Under Pohutakawa, New Zealand Treehouse enthusiasts will swoon over Under Pohutakawa, a snug home nestled in the New Zealand forest not far from the beach front. It has vast glass windows to emphasise the feeling of living among the trees. BBC/Wall to Wall/Jack Dwyer

18/24 Forest ​Under Pohutakawa, New Zealand The site was originally covered in pohutukawa trees, posing a great challenge to the architects who were loathe to cut them down. So, the towers that house the bedrooms are cased in stained wooden battens and the interiors follow suit with light timber walls and furniture. The property itself is surrounded by gnarled tree branches, giving it a fairytale woodland atmosphere. BBC/Wall to Wall/Jack Dwyer

19/24 Mountain House on the Rigi, Swiss Alps Holiday House on the Rigi in the Swiss Alps can only be reached by a 15-minute cable car ride. It sits at 5,500ft above sea level and is a modern take on a Swiss chalet. It is hexagonally-shaped for strength against the blustery elements and lodged into the mountain by a steel chimney core. The pieces had to be brought in by helicopter but once on site, putting them together took just one day. Rex Features

20/24 Coast ​House on the Cliff, Spain Presenters Piers Taylor and Caroline Quentin outside the modern, sprawling House on the Cliff in Spain. This unconventional home is built into a steep cliff face overlooking the Mediterranean. It comes complete with a cantilevered terrace offering maximum sea views and a swimming pool, as well as an unusual Gaudi-esque Zinc tiled roof. BBC/Wall to Wall/Jack Dwyer

21/24 Coast ​Two Hulls, Nova Scotia, Canada Two Hulls in Nova Scotia in Canada is inspired by two ships in dry dock. Jutting dramatically out onto the shore line, they are designated as individual living and sleeping areas. The steel structure is clad with a wooden shell and has glass throughout and the cantilevered trusses were designed to peer over the coast, allowing the sea to pass underneath. BBC/Wall to Wall/Jack Dwyer

22/24 Coast ​Two Hulls, Nova Scotia, Canada Caroline Quentin admires the stylish interior of Two Hulls. BBC/Wall to Wall/Jack Dwyer

23/24 Coast ​Lyngholmen This neatly designed property is only accessible by boat. Hidden on a tiny Norwegian island, Lyngholmen, it's just 100 square metres in size and made to blend in with the rocks. Its roof bridges across them, almost hiding it from sight. BBC/Wall to Wall/Jack Dwyer