John: Finally tonight, from northern Spain, the dying culinary art of making the most expensive cheese in the world.

In this dank, dark cave is some of the world's most prized cheese.

It's where cheesemaker encarni Bada produced the most expensive cheese ever sold at auction, more than $40,000 for a five-pound wheel of Cabrales blue cheese.

>> It's expensive.

There's a lot of publicity, they see you everywhere.

The truth is I've already had people who come because they saw you in Germany or I don't know where, and they come looking for cheese.

John: Authentic Cabrales must sit for months in humid limestone caves, absorbing the unique microflora that gives it its pungent flavor and aroma.

Bada's family has been aging cheese here for decades.

Her daughter-in-law, Eva Gutierrez, follows in her footsteps.

She straps a 44-pound load of cheeses on her back and carries it up a steep, winding foot path to the aging caves in the mountains of northern Spain's asturias region.

>> For us who grew up with it, it's a way of preserving a culture, a tradition that our grandparents and our parents taught us.

I'm continuing with it and I hope my son will too.

At least he'll learn it.

I don't know if he'll make a living from it or not, but learn it, he will.

John: Traditionally, making cheese here has been the work of women.

But the future is uncertain, there are now fewer than 20 artisanal cheesemakers.

>> What can you do?

You think maybe the world's going to end if you don't make your cheese, but it will go on.

Still, it's something you say to yourself, and then, if I stop, there's no more.

John: And that uncertain future could push prices even higher.