Rubén Mendi is a giant pumpkin grower who has consistently broken world records, holding several of the heaviest, most gorgeous specimens of all time. But Rubén did another extraordinary service to his hometown in the Ribera de Navarra, helping it recover several of its abandoned cave homes.

(We asked Rubén for the “secret sauce,” growing giant pumpkins, and he mentioned, among other things, the importance of ventilation. In video: 21:06).

Not long ago, Valtierra had consisted of a hamlet of cave homes, a church, and a castle, but modernity forced cave dwellers out. Now enthusiasts like Mendi are trying to bring them back.

With 10 abandoned caves in the Bardenas Reales (or badlands) of Navarre, Spain, Ruben Mendi wired, plumbed, floored and painted them. He had wanted to revive the naturally heated & cooled little village where some of his ancestors lived because “these houses have some useful lessons for the future.”

Mendi explains that the land was owned by the town —and, as long as they were willing to dig, people could excavate their respective homes. Since these were mostly farmers, or day laborers, the work was done in spare time so it could take a year to dig a starter home: kitchen plus bedroom. As the family grew, new rooms were dug out. The naturally-insulated mountainside keeps the caves at a comfortable temperature year round.

The highly compacted mountain (due to its millions of years of existence) guarantees the safety of the caves. A geologist who did a risk assessment on the structures said that an 8.0 earthquake would knock down the local homes, but the caves would remain standing.

Mendi showed us one of the smaller starter homes — just a bedroom, kitchen and bathroom — as well as the extra large “Palomar” (“Pigeon House”). Palomar was built in 1880 by a local man named Zenón Urbeneta who spent all of his life digging the 250-square-meter (2690 square feet) cave home.

Today, Rubén rents the caves out to visitors, but back in 1850, during the “cave housing boom,” these were affordable, self-dug, off-grid homes for the residents of Valtierra. These are Rubén’s giant pumpkins (he holds several records).