The World's Most Extraordinary Homes

In episode one, their journey starts in the Santa Monica mountains in California, where one homeowner built her dream home from the most unthinkable re-used building material - the wings and tail fins of a disused Boeing 747, which had to be delivered onto the mountain site by helicopter.

Their next stop takes them to the desert Tuscon Mountain Range of Arizona, where Caroline and Piers spend the day and stay overnight in a stunning modern house which is heavily influenced by ancient building methods. The home has an innovative take on traditional rammed earth houses, a centuries-old technique that absorbs the heat during the day and releases it at night, reducing the need for air-conditioning and heating.

Next, Caroline and Piers go to the other side of the world to New Zealand's South Island. Designed to fit within strict planning regulations, the house was inspired by the surrounding trees and mountains and is camouflaged using wooden cedar cladding to cloak the building, and with fireplaces cast in concrete.

The last stop takes them to the Swiss Alps, to a unique alpine chalet. Arriving by cable car, Piers and Caroline discover it's hexagonal shape gives it stability in the freezing winter winds, while the steel chimney core that anchors the house to the mountain also distributes heat around the house. As the mists clear, an incredible panoramic view of the Alps is revealed.

In episode two, Piers and Caroline's journey starts in an ancient Pine forest just outside Madrid, where the architect's brief was to weave this contemporary house among the trees themselves. Clad entirely in basalt and glass, the building reflects the surrounding forest whilst the interior contrasts with incredibly bright primary colours.

Their next stop takes them to the USA and to two houses built in the Catskill Mountains in New York State. The first is a very modern tree house, an upside down three-bedroom home with the living space at the top and bedrooms on the bottom, offering an incredible view over the trees themselves. Nestled into the woods, the house is built on a plot the size of a caravan and clad entirely in glass. The second house is equally modern in design. Arriving by helicopter, Caroline and Piers wander around this high-tech, high-spec imposing structure that was constructed much like a sky scraper. With a double height open-plan living area providing panoramic views of the forest, the structure seems to hang into the forest clearing below.

Piers and Caroline's final stop takes them to Piha in New Zealand, to a house that is built within an indigenous forest of native Pohutukawa trees. Navigating very strict environmental laws, this wooden-cladded and glass-roofed house mimics the branches of the surrounding trees, while its huge sliding glass walls open up completely to allow the surrounding forest to become an intrinsic part of the house itself.

The first stop on their coastal adventure takes Piers and Caroline to an island in Norway, arriving by speed boat for a two day stay in a four bedroom house built on a footprint of just 100 square meters. Built from timber covered with concrete to withstand the extremes of weather as well as the salty atmosphere, Piers and Caroline settle into this beautiful island escape with a swim followed by a barbeque.

Next is Southern Spain, to an unconventional home built into a steep cliff face overlooking the Mediterranean. Caroline and Piers meet the young architects who designed this truly extraordinary building, complete with a cantilevered terrace offering maximum sea views and a swimming pool as well as an unusual Gaudi-esque Zinc tiled roof.

Piers and Caroline head to the other side of the world to the northern tip of New Zealand's South Island in Marlborough Sounds. The three bedroom house is built from two separate wooden cladded structures: a living space with a large dining/kitchen area and the master bedroom, both held aloft by a series of hard wood timbers & linked by a glazed bridge corridor.

Their final stop is Nova Scotia in Canada, to a house 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, the cantilevered trusses were designed to peer over the coast, allowing the sea to pass underneath.

In the final episode Piers and Caroline's journey starts on the Greek island of Anti Paros, to visit a nine-bedroom house that is hidden beneath the landscape and yet still achieves stunning sea views. As they discover, the green roof allows the underground spaces to be invisible so only the pool terrace and white-washed walls are on view.

Their next stop takes them to the lush valleys of the Swiss Alps, where the owner architect made his four-bedroom house so invisible it has to be accessed via a tunnel from the traditional agricultural barn that was already on the site. Piers and Caroline emerge into the main house, its concave façade revealing panoramic views of the surrounding mountains.

Next it's over to New Zealand's South Island, to a house that was built underground to soften the impact on the indigenous landscape while at the same time being heavily engineered to withstand the threat of earthquakes. Dynamite was used to excavate 5,000 cubic metres of earth and rock to create the three-bedroom main house and annex, constructed from concrete and cloaked with an engineered wing-shaped roof.

Lastly, Caroline and Piers cycle to visit a very different underground house nestled in a nature reserve in the outskirts of Amsterdam, Holland. The four-bedroom family house was created by deep excavation and then by stacking the bedrooms and bathrooms across three floors on the north side, allowing for a huge light-filled open-plan living space facing south.