One of the best ways to get to see it´s seaside views is by walking along the La Concha Promenade, 2km long, with many bars and restaurants along the way and benches dotted along.
Visit the incredible Basílica de Santa María del Coro and head inside for even more beautiful features or also visit the Cathedral del Buen Pastor. You can learn about the cultural heritage at Museo de San Telmo, the building itself is just as impressive as a 16th Century Dominican Convent and Renaissance-era.
The City Hall in San Sebastian is a great place to visit, you can see it´s incredible architecture and if you look closely you can still see bullet holes in the exterior of the building as they remain from the Spanish Civil War that took place (1936-1939), you will also find the Alderdi Eder Gardens, a great spot to stop and relax after walking along the Promenade.
Explore the Old Town for the best way to get a feel of its culture, pedestrianized cobblestone streets you can wander around it's many bars and restaurants and enjoy the beautiful views of the Historic Buildings. Many bars offer ´Pintxos´ at lunch and Dinner times, which is also known as Tapas in Spain.
Or for a different outlook you can visit the Plaza de la Constitución with a huge square which was once used as a bullring, but this is now a Neoclassical square filled with crowded bars and restaurants, with more delicious pintxos to try.
Bilbao Airport (BIO) is the closest main airport nearby, only 1 hour 10 minutes away by car and there is a direct bus that can take you to San Sebastián and takes 1 hour 20 minutes.
San Sebastian has a Bus Service which can easily get you around to see the sights.
You can also hire a car or a bike to get around, or by taxi.