A Swedish-Spanish couple turned an inefficient 1980s stucco house in a small Costa Blanca town into a bio-home that heats, cools, waters, and feeds itself, almost entirely on what the land and the sun provide.

The most surprising work is underground. A Canadian well, also called a Provençal well or earth tubes, pulls outside air through pipes buried in the earth, so it arrives in the house at ground temperature. There is no heat pump, no refrigerant, no compressor, only a fan moving air that the soil has already cooled.

On a very hot day, we stood by the vent and felt very cool air coming out, free cooling from the ground. The idea is old, probably beginning in Persia, and here it does the quiet work of an air conditioner without the machinery or the bill.

Anna and Juan bought a home in the town where his family lives. It was an ordinary one for this coast: a plain stucco box from the 1980s, built with little thought for the sun, the heat, or the people inside it.

The house had one thing in its favor, good orientation. Everything else they rebuilt. Cork now wraps the walls set beneath a mineral plaster that lets the walls breathe instead of sealing them shut.

Winter is handled by fire. A thermal fireplace heats the house and doubles as a stove, connected through a wall to the kitchen, so the same flame warms the rooms and cooks the meals.

They capture their own water. Solar panels supply the electricity. And a good share of what ends up on the table is grown in their garden.