Q: How can we travel from Barcelona Airport to Sitges?

A: You have 2 main options:
 
Bus: You can either take the MonBus service which runs from Barcelona Airport Terminal 1, (T1) or

Train: you can take the RENFE train from the airport to El Prat de Llobregat  which is the first stop after Barcelona airport Aeropuerto and then change for a train that takes you to Sitges.

For detailed information on both of these options I recommend you visit our webpage that explains the options in more detail. Here is the link
http://www.barcelona-tourist-guide.com/en/airport/barcelona-airport-transfer.html