Three days – if you go to Sagrada Familia during all day hours, you should book your Sagrada Familia Tour in advance. Because tickets are limited and may have been reserved for a particular time. So, please make your reservation so that you get it for a specific time slot.
A long time – if you go to Sagrada Familia at night and camp in one of the many parking spaces. In that case, you need to plan. Because it is illegal to park in the Sagrada Familia area after 10 PM. you must make a reservation for a parking space earlier (at least a couple of days).
The most complete (and official) guide to Barcelona is Turisme de Barcelona’s Guía del Ocio y la Cultura (Catalan & Spanish). Book and mobile app. This comprehensive guide also includes information about Park Guell Tour, although it focuses mostly on buildings, museums and organisations.
For the mobile phone app, you need to download it from Google Play: Guia de Barcelona. See Barcelona with your Android Phone (Catalan & Spanish).
“This faithful guide to the city explains what’s worth seeing, where to go and how to get somewhere. It has been designed specifically for visitors. And offers a clear overview of the city’s cultural institutions, leisure opportunities and tourist attractions.