It is an impressive sight both during the day and at night. In the daylight you will be able to see the surprising details in the facade, such as the giant turtles right at the base of the structure, and many figures from Christian religion. At night it is lit up with coloured spotlights, creating a different atmosphere from during the day.
If you are visiting around Christmas time you can go to the lovely Christmas market situated directly opposite the Sagrada Familia. It is an atmospheric place with over 200 stalls selling traditional festive ornaments, nativity scenes, decorations and trees.

Actually Francesc del Villar was the original architect of the project, and the proposal was quite a different design to the one we see being built today. The construction of a church of 3 naves, 7 chapels and an 85 metre spire was begun in 1882. There were disagreements between Fransesc del Villar and another architect, Joan Martorell, which led del Villar to resign. Gaudi then stepped in with a brand new proposal, and the Sagrada Familia as we know it was begun.