Douro Valley.

The Douro Valley is the world's oldest demarcated wine region — the boundaries were drawn in 1756, more than a century before Bordeaux's classification — and the landscape inside it has been shaped by terrace-building for almost as long. The river runs east from Porto on the Atlantic coast inland to the Spanish border at Barca d'Alva, and the vineyard country starts at Régua and stretches up the valley for around 100km. Most of the vines grow on schist terraces cut into steep south-facing slopes; the difficult geology is precisely what makes the wine.

Walking holidays in the Douro work best at the Régua-Pinhão-Tua stretch in the middle of the valley, where the terraces are at their most photogenic and the quintas (wine estates) most concentrated. Inntravel's week splits time between Porto and the valley, with bus and train transfers and self-guided walks linking villages above the river. Macs Adventure's two Douro weeks are similar but with a longer in-valley section, and one includes a transfer up to Pinhão specifically to use the Douro railway, which runs along the river's edge between Régua and Pocinho on one of the most-photographed train lines in Europe.

The walking is moderate — the gradients are real (you're going up and down terraced hillsides), but the daily distances are modest, typically 8-15km. Most operators package the holiday around lunch at a working quinta and at least one wine tasting; the food is a serious part of the trip, particularly the regional cabrito (kid goat), bacalhau and the river-caught fish.

Best season is April-June for spring greens and clear weather, or September-October for harvest. July and August are hot — interior Portugal regularly hits the high 30s — though the river makes the valley a few degrees cooler than the surrounding country. Winters are mild but rainy.

For a less active version of the same valley, the Porto-to-Régua train and a one-week river cruise on a small ship gives most of the views without the gradient. Mooch lists the walking weeks for now; cruise options may follow.