The Mathworld page and Wikipedia page for the illumination problem both describe a 24-sided room, which they attribute to "D Castro".
Mathworld's citation is simply:
Castro, D. "Corrections." Quantum 7, 42, Jan. 1997.
This citation has been copied into a few papers and websites. But I can't find any evidence that this paper, the author, or even the journal exists. Where did this polygon really come from?
This is taken from the journal cited: