A non-profit organization promoting mentorship by connecting thousands of academics and professionals with schools in Greece: https://www.thetippingpoint.org.gr/
I am happy to have received excellent feedback after 15 sessions with schools so far!
The largest outreach event I had the honor of contributing to. A 2-day event with games for children, treasure hunt, public outreach talks (including mine on the views on extraterrestrial life and intelligence since antiquity), exhibitions of laboratories, poster sessions, and 3D movies on astronomy!
https://www.unige.ch/cite/evenements/250-ans-de-lobservatoire-de-geneve
Check the schedule in the website of the Skinakas Observatory in Crete: http://skinakas.physics.uoc.gr/en/
Professors and PhD students (like me before) will guide you to astronomy and the research of the group.
If you visit my hometown, don't miss the astronomy club in the area! http://users.sch.gr/geoto/index.htm
It is my honor to have contributed in one of their Summer Schools and other public outreach activities!