The three-day festival of All Saints and Souls Days honor the dearly departed by visiting them in their final resting places. And as such it has nothing to do with trick or treat. Because of Spaniards flocking to the cemeteries, local governments offer extra bus services. In Madrid, the municipal government has acted in character. See the extra bus services here.
All Saints Day, the big day of the dead on 1 November, is festive-solemn as only the Spaniards can make it.
Spain is gearing up for the festivity that is somewhat confusing. It’s a feast that’s celebrated in a very personal way. A special day for communing with the deceased relatives, telling them they haven't been forgotten. But wait a minute, what they're actually celebrating is All Souls Day which in Spanish is Dia de los Muertos, i.e., Day of the Dead, and, strictly speaking, it falls on 2 November! People celebrate ALL SOULS DAY on 1 November which is ALL SAINTS DAY. So there's a bit of confusion here. . .
“The history of Spain is engraved on its tombstones”