On a cold, windy, rainy day when I would have prefered to stay in bed, we ventured to the Sagrada Familia. It was worth braving the cold. We booked a guided tour and this is highly recommended. There is so much history and so many details that are lost without the focus of a professional guide.
It is best to buy tickets online. They are timed. Although we were admitted 30 minutes early, we understand this is unusual. The line to buy same day tickets was unbelievably long considering the weather. Best to avoid the line that is sure to be hours long in good weather.
There are many websites selling tickets. We were scammed on the first purchase by a third party seller - and the site seemed to be the official one. Buyer beware. Here is the official site. https://sagradafamilia.org/en/
Some highlights.