The Basque History of the World by Mark Kurlansky (1999) is an entertaining and wide-ranging account of the Basque people — their language, culture, politics, history, and food. Kurlansky is a journalist with a gift for narrative, and the book covers everything from Basque whalers who reached Newfoundland before Columbus to the origins of pintxos. Required reading before visiting the Basque Country.
The Lamentations of Zeno by Ilija Trojanow is set largely at a climate conference in San Sebastián and captures the city's strange mix of elegance and melancholy. Not a travel book but an excellent novel in which the city plays a real role.
A Late Dinner by Paul Richardson (2007) is a beautifully written account of Spanish food culture, with substantial sections on Basque cuisine, the nueva cocina movement, and the restaurant world of San Sebastián. Richardson writes with genuine understanding of what makes Basque cooking distinctive and why it matters.
Guernica by Dave Boling is a historical novel about the Basque Country and the bombing of Guernica in 1937, tracing several generations of a family from San Sebastián through the Spanish Civil War. It's accessible historical fiction that puts the city's 20th-century political history into human terms.