There are bus services which you can book in advance of your trip that run between Barcelona Airport And Castelldefels. This gives you the security to know you have your transport arranged and booked in advance of your trip.
How to make your booking
You can book your bus transport service between Barcelona Airport to Castelldefels online. The bus service may either be a minibus or a coach service depending on the number of people needing the service on the day. After you make your booking you would need to print out the booking voucher.
On the day of your travel make sure to bring your booking voucher with you and present it to the bus representative at the designated meeting point at Barcelona Airport. You will know the exact meeting point after you make your booking.
Each person can bring one large suitcase and one carry on bag with you. If you have more luggage than this you would need to indicate this when you make your booking and there would be a supplementary charge for each additional bag.
Bus transfer with fixed drop off point
This bus transfer service is low cost and has a set drop off point in Castelldefels centre. From the drop off point you would make your way to your accommodation.
Journey Time: 1h to 2h (depending on traffic)
Book at least 48 hours in advance.
Private transfer to / from Castelldefels
There is also a private transfer service from Barcelona Airport to/from Castelldefels centre