I'll be visiting Northern Spain in September and read about some festivals that I could possibly visit.

Has anyone heard of these festivals and can confirm the dates?

Are there any more in mid-late September that would be interesting?

Tarragona:
Festa de Sant Tecia, Sept 23
According to Rough Guide there are gigantes & human castles (?).

Barcelona:
Festa de la Merce, Sept 22-25