Santa Clara Island sits in the middle of La Concha bay, close enough to swim to from the beach (it's about 700 metres from shore) but far enough to make it feel like a genuine escape. A small lighthouse, some basic beach facilities, and a lighthouse keeper's cottage are all that stands on the island, which is surrounded by flat rocks and a small sandy beach on the sheltered southern side.
The municipal boat service runs to the island from the harbour in summer (the crossing takes ten minutes), but hardy swimmers simply swim out — the water is calm within the bay, and the return swim with the city panorama ahead of you is one of the more pleasurable things you can do in San Sebastián. The island is small enough to walk around in twenty minutes; the rocks on the northern side face directly into the Atlantic and are spectacular in rough weather. The beach on the south side gets packed on summer weekends; weekday mornings are far quieter.