ARRIVAL: Enter to the car park and take the ticket at the entrance. Park in any free space. Go to the office with your reservation and the ticket. The parking stuff will give you the card which allows you to enter and exit several times.
DEPARTURE: Use the intercom and give your reservation number so that the staff can open the exit barrier.
IF YOUR BOOKING ALLOWS UNLIMITED ENTRANCE AND EXIT: use the multipass card/device the staff gave you.
Avenida de la Ciudad de Barcelona 152
Calle de Téllez 25