This cider is unlike typical American cider - this stuff is less sweet, and almost tastes crispier and more natural. Sidra dates back to ancient times and is still popular today.
People can go to sidrerias where they serve the cider. Traditionally, sidra is served all the way up in the air into a glass in order to create more carbonation.
Check out my two photos below:
You can watch a video of the process here:
Without the spectacle (no, really - the whole bar was laughing at us), it is normally served with a tap that shoots the cider into your glass (see photo below of me). You traditionally only drink about 1 inch at a time because you don't want it to get warm. You are not supposed to let it sit at all.
Here's a photo of a guy pouring sidra in the traditional garb of Asturias.
So go find some sidra asturiana - es deliciosa!
Photo credit: http://www.telecable.es/personales/jjdr1/cultura_sidra.htm