Two churches in Barcelona. Church of Colònia Güell has 1 ticket or tour to book; Sagrada Familia has 125 tickets and tours to book. The table and the two notes below put them side by side; the full pages have what to see, the ticket and the timing for each.
The Crypt of Colònia Güell stands in the industrial colony of Colònia Güell, in Santa Coloma de Cervelló, about twenty kilometres south-west of Barcelona, and a ticket is required, covering the crypt, the interpretation centre and a walk through the colony, with an audio guide. It is one of Antoni Gaudí's most innovative works and part of the UNESCO World Heritage listing of Gaudí's works.
Every ticket here is timed and almost every one sells out days ahead, so booking is not optional. The base ticket covers the church and the crypt where Gaudi is buried. Adding an audio guide costs a few euros more and is worth it, because nothing inside is labelled. A guided tour in a group of about twenty costs roughly double the base ticket and lasts an hour, after which you may stay on alone.