All great artists need to practice and Gaudí was not an exception. Unfortunately, for an architect, it is a bit more difficult to do some experiments since it requires some extra space than other type of disciplines.
La Colonia Güell was a big textile factory from Eusebi Güell. All families working in the factory used to live there and they had all the facilities needed to live (like a school, food court, hospital and even a church).
Fortunately, Gaudí used the space in la Colonia Güell to try some techniques that he would apply later in la Sagrada Familia. He built the crypt of the church. However he did not finish the buildings since Eusebi Güell died in 1918 and his relatives did not want to continue the project.
La Colonia Güell is around 10 km outside Barcelona and can be reached by car, bus, or train in around 30 min from Barcelona.