A long time ago, there was such a thread in the e-Sangha meditation forum, if you remember.
I've considered starting such a thread here, but I'm not sure what to write. I also didn't want to start a thread, "A meditation challenge?" asking people how to write it, because then whoever reads it wouldn't likely follow it, because the challenge wouldn't be determined for several posts or several pages.
Perhaps one of Dhamma Wheel's staff has an idea for such a thread?

