Santander is the nearest ferry port to the Picos de Europa. Brittany Ferries sail from Plymouth and Portsmouth to Santander.
P&O Ferries sail from Portsmouth to Bilbao, an hour's drive from Santander.
And LD Lines now have new routes running from 2014, Poole to either Santander or Gijón.
Also, AFerry.co.uk is a useful website where you can compare prices and read reviews for ferries to Spain.
Add interest to your crossings by looking out for whales, dolphins and seabirds. Visit the Company of Whales and Orca websites for information on the possible cetaceans to be seen in the Bay of Biscay.
Santander also has the closest airport to the Picos de Europa. Ryanair is currently the only company flying from the U.K. (London Stansted and now Edinburgh too) and Eire (Dublin) into Santander. For Belgian and Dutch visitors there are also flights with the same company from Brussels to Santander.
From the U.K. - A more environmentally-friendly way to travel to Spain if you want to avoid flying. Information from the man who knows all about European train travel, the man in Seat 61, rail to San Sebastian/Donostia. From there you can get a bus to Bilbao where you can be collected.
From Madrid - the most direct route to drive is via Segovia, Valladolid, Palencia, Aguilar de Campoo, Cervera de Pisuerga, over the Piedraslenguas pass bringing you down to Potes in the east of the Picos.
From France - from Bordeaux/Biarritz, crossing the border at Irún in the Basque country, take the A8 motorway past Santander and Torrelavega to Unquera, then turn onto the N 621 for Panes. Here you can head either to Potes and the eastern Picos, or to Cabrales and Cangas de Onis and the western Picos.