Over the years, I've made a point of being in Spain at Easter, or in June (for the Hogueras festival in Alicante). May isn't a time where I've done much travelling in Spain, so I have no first hand experience of these:

Major festivals when you are there are

Madrid - festival of San Isidro, 14th - 18th May
Basic info in English

Alicante region, Petrer - Moors and Christians, 14th - 18th May
Fiestas de Moros y Cristianos (also called festival of Saint Bonifacio)
http://www.petrer.es/portalPetrer/fd...o=6&nivel=1400
(dedicated festival website for Petrer here)

Gerona region, Ripoll (to the North of Barcelona) - Wool festival, 17th May
Fiesta de la Lana/Festa de la Llana
http://www.ajripoll.org/ciutat/vila5.htm
I can't guarantee the date is correct, if you are interested in going please email the tourist office first - http://www.ajripoll.org/ciutat/vila5.htm


I've included Petrer even though it is a bit of a detour because the Moors & Christians festivals in the Alicante region are so celebrated. I've not been to these ones in Petrer, but the ones in Alcoy and Crevillente are hugely enjoyable and very spectacular. They are also VERY NOISY!!!