Indeed, it is "La Diada" (short for La Diada nacional de Catalunya)
We were all on holiday here that dreaded day. All celebrations were cancelled the moment it was confirmed the crashes were no accidents.
But life goes on, and today is indeed the national holiday of Catalunya, which is, itself, a part of Spain.
Daniel
PS: BTW thanks for remembering Beetle, this holiday has been somewhat, and comprensibly, buried under all that happened on 2001.