Alderdi Eder, Public park in San Sebastián, Spain.

Alderdi Eder stretches along the Concha Bay waterfront with paved walkways, manicured gardens, and numerous trees providing natural shade throughout. The space connects different sections through broad promenades and offers ample room for walking and outdoor activity.

The park was laid out in 1880 on former army training grounds outside the city walls, a plot then known as Errege Soro. After the army sold the land to the city, the name Alderdi Eder, proposed by Serafín Baroja, was made official on 28 May 1879. In 1887 a casino by Luis Aladrén Mendivil and Adolfo Morales de los Ríos was built on the grounds; it later became the city hall, prompting a reworking of the whole area.

The name Alderdi Eder means "beautiful place" in Basque and was given to the park by the writer Serafín Baroja. The city officially adopted it on 28 May 1879, after the army sold the land to the municipality. The gardens stand between the town hall and the Concha Bay.

The park sits near major transportation hubs and is equipped with benches, water fountains, and play areas. Access is available from early morning and the space remains open into the evening hours.

The park's name was coined by writer Serafín Baroja, father of novelist Pío Baroja, and the city officially adopted it on 28 May 1879 after the army sold the land to the municipality. Before that the grounds were royal manoeuvre fields called Errege Soro, outside the old walls.