Finca Guell,

From the outside it looks quite impressive with that large metal dragoon guarding the gate. Inside it it is a run down park with limited options. You will find a small museum with a display of concrete blender, minor tools and some explaining drawing hence Guells work. A small theatre with a video is accessible to all. Paying 5 EURO to enter is probably the most wasted money for years. That said in the next 5 year period there are plans that will improve "things" seen from a touristic angle and paying more respect and credit to Guell.
Been there done that, will not return.

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All there is to see is really the gate. 5€ isn't much but better spend it on a beer. As mentioned before, definitively a rip off
There is really nothing inside. Wouldn't even call it a park, landscaping is run down, small map from 100 years go shows a large park but only about 10% is left in the area accessible after paying so there anout 10 m x 30 m of wasteland to see. There is a larger park nearby totally free.
Skip this one.

Fascinating gate house designed by Gaudi. It is being slowly restored, financed by the 5 euro entry which I personally think is well worth it to help maintain such an important site. The garden contains a lovely little nature reserve where you can see wildflowers and even little lizards scurrying about! The people that work there are enthusiastic and very helpful, keen to explain everything about the gatehouse. Well worth a visit!