I just bought tickets to Sagrada Familia and they sent an email that recommended Colonia Güell. Was this worth visiting? If so, how how long were you there? I have 3.5 days in Barcelona so just wondering if it should be something to consider. Any other recommendations would be greatly appreciated as well.
It's one of the first works from Gaudí and it's located in the outskirts of the city, in the town of Santa Maria de Cervelló. More info here: http://infocatalonia.eu/w/0Mug3
In any case, you need to assume that in 3.5 days you won't see much of everything there's to see in Barcelona, so do choose your venues carefully.