San Juan de Gaztelugatxe is convenient to reach from Bermeo, Mundaka, and Bizkaia.
This was an island (cay) just off, by maybe 20 meters, the Basque coastline. A couple of centuries ago, an artificial stone bridge was constructed and a small church was erected at the end of approximately 240 winding steps from the bridge.
This is a nice free place to bring kids for the picture value, and even the elderly can make the hike up the stairs. Do bring sunblock on a sunny day, however, as the sun will leave its mark on you should you not be careful.
Those people who enjoy cold-water swimming will find the water around the bridge area to be quite lovely.