Halloween in not a Spanish tradition, but people do celebrate this. They celebrate it the same way as in other places in Europe. People dress up in all kinds of different costumes. Halloween is the place to wear fancy dresses with scary masks or to dress like ghosts, zombies, witches and much more. With Halloween you can be unrecognizable. This is the same as with carnival. People celebrate it at home with some friends or go to a club or bar where they have special theme nights. Also hotels sometimes arrange special Halloween parties.
When people hear the world Halloween they automatically think about the USA. Halloween originally was founded in Celtic Britain. The people of Britain worshipped gods of nature and lived in Isles during ancient times. Two festivals were important in the Celtic calendar. These two festivals are; Samhain and Beltane. The Samhain celebrated the start of the winter and the other festival celebrates the start of the summer. The Celtic people believed that there were spirits from a dead rose in tomb. To drive the ghosts away they wear scary costumes. This started on the 31th of October. The Celtic people were afraid of the winter. During the winter the days were cold and short and the nights were long. They thought that the winter was associated with evil spirits and death.
Some nightclub like Shoko or Opium also celebrate this party. But there are many more. When you are in Barcelona before the period of Halloween, you will see some events which are promoted. You also can search on the internet to different clubs and see what they have to offer. You can go to a big club or just a little café. This depends on your own interest what you like the most. The interior of the club is decorated with things which relate to Halloween. The crew also wears a Halloween outfit. The people who come to this party also wear costumes. Of course there are always people who don´t disguise. It is just a reason to go a night out, dress up and party.
So do not wait, book your accommodation in Barcelona and buy your Halloween outfit.