I've facilitated a couple of code retreats before and would be more than happy to do so again. We'd need a space to hold it, and it would be great if we could find some sponsors to provide lunch?
Code Retreat is a fun day, giving people the chance to sharpen their dev skills. You spend 45 mins pairing on Conway's Game of Life, TDD is expected, to see how far you can get. After the 45 minutes is up you delete your code, everyone comes together to reflect before pairing up with someone else and trying again.
Each round will add different constraints, e.g. TDD as if you mean it.