Urdaibai Biosphere Reserve

Urdaibai is the estuary of the Oka, declared a biosphere reserve by UNESCO in 1984, covering about 220 square kilometres of tidal marsh, sandbank, holm oak wood and cliff between Gernika and the sea. The marshes are a major stopover on the Atlantic migration route, with a bird centre at the old Orueta school. At the estuary mouth, the sandbar off Mundaka produces a long left-hand wave that is among the best known in Europe and has hosted world tour events, though it depends on the sand and has failed in some years. San Juan de Gaztelugatxe, an islet reached by a stone causeway and 241 steps to a hermitage, lies just outside the reserve and requires booked entry. Gernika, at the head, holds the Basque assembly oak.

What you actually see

• The tidal marshes - migration stopover habitat at the head of the estuary.
• The Mundaka wave - a long left-hander off the sandbar at the mouth.
• Gaztelugatxe - a causeway and 241 steps to an islet hermitage nearby.
• The Gernika oak - the tree under which Basque assemblies met.

When to go

April to June and September to November for birds and mild weather; the Mundaka wave works best from autumn to spring with the right swell and sand. Gaztelugatxe requires free booked tickets with a daily cap.

Honest expectations

Gaztelugatxe access is capped and must be booked in advance, with the steps steep and exposed. The Mundaka wave is inconsistent and has disappeared for whole seasons after dredging changed the sandbar. Rain is frequent.

Nearby

Gernika and its peace museum are at the head; Bermeo and the coast lie north.