In the courtyard of the Casa de Juntas stands the oak tree that has symbolised Basque self-government since the Middle Ages. For centuries the lords of Biscay — and later the Spanish kings themselves — swore here to respect the fueros, the local rights and privileges of the Basque people. When Hitler bombed the town in 1937, the tree was the one civic landmark that the Condor Legion was specifically ordered to spare; it survived.
A small classical pavilion shelters the petrified trunk of the previous tree, and a glass case displays acorns descended from the original. The current oak — the fourth generation — was planted in 2015. Tourist visits are free and the Casa de Juntas next door includes the political history.