Check the tide and walk the causeway across to the island of San Nicolás

Go into the basilica of Santa María and look at the altarpiece, among the largest in Spain

Watch the boats come in and work out what a working Basque fishing port still looks like

Find out what the Antzar Eguna in September is and how it is done now

Walk the coast path along the cliffs either side of the town

Lekeitio has two beaches with the island of San Nicolás between them, and at low tide a stone causeway comes out of the water so you can walk across to it. The town is a working fishing port with a late Gothic basilica whose altarpiece is one of the largest in Spain. Its September festival includes the Antzar Eguna, in which crews in boats grab at a goose suspended over the harbour — now done with a dead bird, having been done otherwise for a very long time, which is the sort of thing Basque coastal towns do not apologise for.

Lekeitio: A Fishing Town and an Island

Stand between the puente viejo and Calatrava's footbridge and work out how many centuries are in view

Find out what Alfonso XI granted the town in 1335 and what the bridge had to do with it

Walk the old quarter stacked up the hill above the port

Watch the fleet unload — this is one of the main fishing ports on the Cantabrian coast

Walk round to Arrigorri beach at the mouth of the ría

Alfonso XI granted Ondarroa the rights to the traffic over the wooden bridge across the Artibai in 1335, and the stone bridge that replaced it in the 18th century — the puente viejo — is still standing. Beside it Santiago Calatrava built a white asymmetric footbridge in the 1990s, so a working Basque fishing town has a 14th-century charter, an 18th-century bridge and a piece of late-20th-century engineering all within a hundred metres. The port is among the most important on the Cantabrian coast and the old quarter is packed onto the slope above it.

Ondarroa: A Bridge by Calatrava in a Fishing Town

Go to the Casa de Juntas and find the oak under which the fueros were sworn

Go through the Peace Museum, which reconstructs what 26 April 1937 was actually like from inside the town

Work out what was claimed afterwards — that the Basques burned their own town — and how long that lie survived

Find the reproduction of Picasso's Guernica in the town, and work out why the original is not here

Work out why this town and not another: it was the symbol of Basque self-government, and it was market day

Gernika was the symbolic seat of Basque law — the lords of Biscay swore to respect the fueros under an oak tree here. On Monday 26 April 1937 the German Condor Legion and the Italian Aviazione Legionaria bombed the town on market day. It held about five thousand people plus refugees, perhaps ten thousand in all. The rebel side then claimed for decades that the Basques had burned their own town, a lie that outlasted the war and the dictatorship. Picasso painted Guernica that year, and the town has been a byword for the bombing of civilians ever since.

Gernika: The Oak Tree and the Bombing

Get to a hide on the marshes on a rising tide, which is when the waders come in off the flats

Work out the three bands — mountain, marsh and cliff coast — and how far apart they actually are

Go to the Urdaibai Bird Center at Gautegiz Arteaga for the ringing and the counts

Work out the scale: 22,452 hectares, about a tenth of Biscay, protected since 1984

Walk out to the cliffs and islands at the mouth, which are the seaward end of the same reserve

Urdaibai is the estuary of the Oka behind Gernika — 22,452 hectares, about 10% of the whole of Biscay, made a UNESCO Biosphere Reserve in 1984. It is the most important wetland in the Basque Country by size and condition and a major resting and wintering ground for migrating birds, which is why it was declared a Special Protection Area for birds in 1994 and added to the Ramsar list. It works as three bands running into each other: the mountain, the flats and marshes, and the coast with its cliffs, ports and beaches, and between them they hold the greatest diversity of landscape in the Basque Country.

Urdaibai: The Estuary Behind Gernika

Work out what Head of Biscay meant and what Bermeo lost when it stopped being it in 1602

Go into the Torre Ercilla for the fishermen's museum, which is the town's actual history

Find the Puerta de San Juan, the last surviving gate of the medieval walls

Watch the fleet work the old port, where nearly the whole town still lives

Walk out to the Atalaya and look along the coast towards Matxitxako and Gaztelugatxe

Bermeo was founded in 1236 and held the title of Head of Biscay from 1476 to 1602 — the principal town of the whole lordship, with privileges to match and the leading voice in the Juntas Generales. It lost the title to Bilbao and never got it back. The old port is still one of the most important fishing harbours on the Cantabrian coast, ninety-five per cent of the population lives round it, and Gaztelugatxe is just along the coast. The Torre Ercilla holds the fishermen's museum.

Bermeo: The Head of Biscay

Take a boat tour to see the Flysch cliffs

Hike the coastal path from Deba to Zumaia

At the Algorri cliffs, find the thin black clay line cutting through the rock — the Cretaceous-Paleogene boundary, the asteroid impact layer that ended the age of dinosaurs 66 million years ago

The cliffs between Deba and Zumaia expose about sixty million years of seabed standing on end — layer after layer of rock tilted upright by the collision that raised the Pyrenees, so you walk along the beach and cross the millennia one stratum at a time. That makes this one of the most complete continuous rock records anywhere, and geologists come from all over the world for it. At Algorri there is a thin dark clay line in the rock face: the iridium layer left by the asteroid that ended the Cretaceous 66 million years ago, visible as a band you can put your finger on.

Zumaia: Sixty Million Years of Flysch on End

Ride or walk a vía verde end to end and notice that the gradient never really changes

Work out why: the route is a railway grade, and a steam locomotive could not pull anything steeper

Go through the tunnels and over the viaducts, which are the original railway structures

Find the old station buildings on the route and see what they have been turned into

Work out which line this was, when it closed, and what it was carrying

Spain closed a great many branch lines and mining railways in the 20th century, and rather than let the trackbeds go the country turned them into the Vías Verdes — surfaced, waymarked routes for walking, cycling and riding, on grades no steeper than a steam locomotive could pull. That constraint is the point: they are almost flat, they go through the tunnels and over the viaducts the engineers built, and they make otherwise serious terrain accessible to anyone. The Ferrocarriles Vascongados route runs 13.6 kilometres between Soraluze-Placencia de las Armas and Anzuola.

Vías Verdes: Riding Spain's Abandoned Railways

Stand in front of Oteiza's facade and count the apostles — there are fourteen, which is two too many

Work out why the frieze is at road level: the facade starts below the path you arrive on

Find Chillida's doors and then Lucio Muñoz's apse inside

Go down into the crypt for Basterretxea's wall paintings

Work out what it means that a religious building of 1950 was given to the artists it was given to

In April 1950 the Franciscan provincial proposed a new basilica at Arantzazu, high in the Gipuzkoan mountains, and the job went to the architects Sáenz de Oíza and Luis Laorga. What is remarkable is who else worked on it: Jorge Oteiza carved the main facade, with a frieze of fourteen apostles set at road level because the front starts below the path; Eduardo Chillida made the main doors; Lucio Muñoz painted the apse; Néstor Basterretxea did the crypt walls and Xabier Egaña the murals. It is effectively the Basque avant-garde of the 20th century working on one building.