Caroline Quentin and Piers Taylor round off their tour with a visit to some subterranean stunners.

They begin on the Greek island of Antiparos with a poke around a nine-bedroom holiday home nestling in the hillside with gleaming white walls peeking through.

In the Swiss Alps Caroline and Piers head to the village of Vals, where an apparently ordinary barn sits atop the entrance to another underground wonder; and in New Zealand they marvel at a house designed to work in harmony with the landscape’s fragile natural beauty.

Finally, they’re in Amsterdam, delighted by an eco-friendly ‘hobbit house’ full of quirky, reclaimed objects – including a Daimler repurposed as a cupboard!