The nearest airport is in Santander, but most flights are domestic, primarily from Madrid. International flights from London, Dublin, Rome, Milan, Frankfurt, Paris and Amsterdam. Other international flights to Bilbao.
Arrival by ferry from UK is also possible in Santander. There is a ferry terminal.
Since many interesting places are outside the main city Santander in small villages in the country side a car is recommendable. Alternatively public buses are available to larger towns. Frequent public buses are available between Santander and Bilbao.
You can surf at the beaches of Somo, Los Locos in Suances near Torrelavega and Meron in San Vicente de la Barquera.
If you are coming from the Basque Country the logical continuation is to go to Asturias. Just follow the coastline westwards.