Short notice, but here goes nothing:

I'm giving blood at the new-ish Red Cross (DRK) blood center in the Alexa mall at 11:30 this Friday the 9th.

They still have available appointments right before, right after, and at that same time. They're probably rather walk-in friendly too. I've heard they don't often feel comfortable with donors under roughly the B1 German language level, though.

I know not everyone can give blood for a huge variety of reasons — donate at your own risk, I assume no liability for supplying this information, etc. — but if you can't give, there will at least be a Kurzgesagt fan having a mandatory snack in the vicinity afterwards. I plan to wear last year's red Project for Awesome shirt if you need help spotting me. Bonus points if you're familiar with the P4A too!