We found this skull on a beach in southwestern Sweden, and are curious as to what kind of animal it was.
It's definitely a bird pelvis (synsacrum). Based on the size (~30 cm), it came from a very large bird. Unfortunately, comparative images of bird pelves are rare on the internet. Some possibilities (large birds of Sweden possibly found on the coast):
A loon skeleton (from http://paolov.wordpress.com/2011/08/05/friday-mystery-object-107/) shown below.