Spain is a traditionally catholic country therefore many catholic customs have endured the passage of time and have survived up to the 21st century. One of these customs is the tradition of the processions which are celebrated at different dates throughout the year and take place throughout the whole country, most of the time during festivities, with Easter being the time most of the processions are celebrated.
If you are in Spain and you come across one of this processions do stick around and watch it, it is not a bad thing to watch even if you aren’t a catholic (I myself am not a very religious person yet I enjoyed some of the ones I’ve seen and others at least I found curious). The most interesting ones are the ones in the southern part of the country since the people who participate on them are more vocal in expressing their devotion to the patron, the virgin or Jesus and ambient surrounding them is more festive, you might even here some flamenco songs, before, after or even during the processions (this last case is more rare since during the procession people normally shout praises), as well as a party since outside of easter these procession normally happen during festivities.
That being said all throughout the people from different zones have different traditions for these kinds of things so you may find another that is more to your liking than that one. One downside though is that even if you don’t take part on the tradition since they tend to interfere with the traffic, so if you are in a bigger city and you want to go somewhere else in public transport (I don’t recommend taking a taxi during those days) or by car do calculate that it may take you some more time to reach your destination either because of traffic or because you may need to walk.
In case you are wondering the people you see in the image above are “Cofrades”, the members of the christian confraternities “Cofradías” that usually parades whichever patron, virgin or Christ that is being celebrated that day. The people who carry the Virgin, Saint etc are the “Costaleros”, who are also “cofrades” of the confraternity.
Here are some images: