La Sagrada Familia was started in 1882 on March 19th in the La Sagrada Familia Square. It is a massive building that attracts many tourists all over the world. La Sagrada Familia, in English, means "The Sacred Family," for it pertains to the family of Jesus Christ, Joseph, and Mother Mary.
It is still under construction because of Gaudi's untimely death (he was run over by a tram), so La Sagrada Familia is estimated to be completed in 2026. This is a very vague estimation, as all money paid for the construction and completion of La Sagrada Familia comes from tourist funds.
Construction is still going on because the construction workers are following Gaudi's original plan, which is highly expensive. They only get money from donations and tour fees, so they don't have enough money to finish because of Gaudi's untimely death (he was run over by a tram) but it is estimated that it will be completed in 2026.
When it is done, it will have 18 towers: 12 to represent the apostles, 4 to represent the evangelists (these towers will have animal carvings at the top), one shorter one for Mother Mary, and the tallest will have a cross on the top, representing Jesus Christ.