Donostia has a beautiful Island called Santa Clara Island to which you can get:

• Motorcycles from the port:  https://shop.sansebastianturismoa.eus/
• Renting a kayak at the Royal Tennis Club of San Sebastian School of the Sea: https://rctss.com/actividades-del-mar-escuela/ 

Within it there is a small beach, a merender and a lighthouse.

In the interior of the lighthouse, the sculptor Cristina Iglesias has made an installation called Hondalea that represents the sea, its wave and the movement of the water when it hits the rocks.