My suggestion: go with the thought that you're going to a Park (after all, that is the name of it, yes?), rather than a museum or a major tourist-site. While the Gaudi museum does sit on the grounds, the museum is actually Gaudi's former home, and so, it's not a typical museum, but instead, a very small and quaint dwelling. The park itself is quite beautiful, though, and certainly worth the trip. Unique and different from most parks we frequent, showcased by the famous mosaic serpentine wall, which surrounds a lovely plaza and provides a perfect perch for beautiful views of Barcelona. Paths leading away from the plaza meander along greenery, flowers and trees. There are benches in quiet spots (perfect for a picnic of bocadillos and cava), and a full outdoor cafe serving yummy ice cream treats, and - of course - cervezas, perfect thirst quenching on a hot day.