La Sagrada Familia

The basilica is considered to be Antoni Gaudi's significant architectural achievement.

An excerpt from the article 22 facts about La Sagrada Familia
Antoni Gaudi was a Catalan architect and engineer of Art Nouveau (a direction in architecture in the late 19th and early 20th centuries), famous for his exceptional designs. A turning point in Gaudi's artistic life was meeting with the Barcelona industrialist Eusebi Güell, with whom the architect became friends. Güell greatly appreciated Gaudi's art and financed many of his projects. Gaudi created many buildings for him, including a hunting pavilion and a church. He also did commissions for the church and, in total, did about 20 major projects, mainly in and around Barcelona.