Question: What is there to see in Barcelona that is a structure opened prior to 24 September 1957?
Answer(s):
answer: Palau de la Música Catalana
answer: Park Güell
answer: Casa Milà
answer: Museu Nacional d'Art de Catalunya

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ns:m.01f62)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
ns:m.01f62 ns:travel.travel_destination.tourist_attractions ?x .
?x ns:architecture.structure.opened ?num .
FILTER (?num < "1957-09-24"^^xsd:dateTime) . 
}