The Meetup (as in Meetup.com) event, for wider circulation, more RSVPs, and comments:
https://www.meetup.com/Effective-Altruism-Madrid/events/280985279/
I will be there a bit in advance, and spread out a modest "ACX Meetup" banner somewhere in the Puppet Theatre.
You're right! And yes, it's on the other side of the park, so apart from (perhaps) slightly higher occupancy of the park than usual, we should not notice it. (And the book fair will be an excellent activity for those with time and energy to stay in the park after our meetup! → https://www.ferialibromadrid.com/ )
I did check that the there are no events at the puppet theatre at that date and time, btw.
Important: (repeating what's on the description already, to perhaps trigger notifications for all attendees): if it's rainy, or if El Retiro park is closed due to strong wind gusts, we'll meet at this bar instead (it's ~1km away from the Puppet Theatre, on the other side of the park): https://cruzblancalasmurallas.com/ https://maps.app.goo.gl/Yy2PPhjkLkud3iDV9