Thursday is a national holiday in Spain, a Red Day, el día de la Asunción de la Virgen María, celebrated on 15 August each year.
As for local holidays, Castell de Guadalest celebrates on Wednesday, so if you’re planning a midweek trip that might be a little busier than usual.
Because of the national holiday on Thursday, many places are also taking Friday as a local holiday, and some businesses in other areas closing as a bridging day, so if you have anything important planned, check they are open. There are far too many places to mention, but a few notable local holidays are Bigastro, Denia, Guadalest again, and Callosa de Segura.
Another word of warning in that Tuesday is 13th of August, and Tuesday the 13th has a similar significance in Spain as Friday 13th! Don’t go out is the advice! Or get married!