Evening group activities in Athens in October?

I'm helping to organize a medical conference in Athens in early October and am looking for ideas for evening social activities for a group (probably 50-60 people total, though we could break up into smaller groups). It looks like the Acropolis closes at 6:30, which wouldn't work since the conference closes only at 5:00. If you have any ideas, please let me know! The conference is in central Athens.