The Tower of the Swallow and the rest of La trilogía blanca by Eva García Sáenz de Urabayén. Three crime novels set in Vitoria-Gasteiz that turn the city's medieval streets, dolmens, and dark history into the backdrop for a detective story. Best read after walking the routes.
Patria by Fernando Aramburu. Not set in Vitoria but in a fictional Basque village an hour or two away. The novel follows two families across the decades of ETA's armed campaign and is the most acclaimed Basque novel of the 21st century — essential context for understanding modern Basque politics.
The Spy of the First Person by Sam Shepard. The American playwright spent time in Vitoria's hospitals during the late stages of his ALS; his last book is in part a meditation written from a city that he barely names but clearly loved.