Even though it has star players and historic clubs, La Liga is one of the most predictable leagues in terms of champions. Their domestic cup, the Copa del Rey, isn't very different, even though there is more variety in the champions you still don't see deep runs from lower division teams like you do in other countries.
In the 2001/02 season we saw the exception that confirms the rule. UE Figueres, a team from a town of 46,000 people who has never featured in the Spanish top flight, made it to the semi-finals eliminating all-powerful Barcelona along the way.
Figueres had advanced from a preliminary round and faced Barcelona right away in the round of 64. They pulled off the miracle with a narrow 1-0 victory at home in front of a crowd of around 9,500 fans, scoring the goal in overtime. What makes this win even more impressive is that Barcelona did not rest any of their stars, big names such as Xavi, Puyol, Saviola and Giovanni all played.
Figueres would then have a sequence of lucky draws, facing Osasuna (17th in La Liga) in the round of 32, and then lower division clubs Novelda and Cordoba. Eventually, after advancing 3 more times, Figueres became the first third division club in Copa del Rey history to reach the semi finals. For context the tournament was on it's 99th edition.
UE Figueres would eventually lose to Deportivo La Coruña in the semis, who would go on to lift the trophy, but their deep cup run and colossal upset against Barcelona will never be forgotten.