My longarm group does a challenge every year.
Last year our challenge was defined with these requirements:
1) No piecing
2) 40" square
3) 100% cotton or Dupioni silk
Other than that, sky's the limit.
My inspiration came from the Cosmati Pavement in the Westminster Abbey (it was restored just shortly prior to Prince William's marriage to Kate Middleton - they stood on it for their ceremony).
Anyway, I stumbled across it, downloaded LOTS of pictures, then drew out my design. It's not exactly the same, but whenever someone asks, I tell them my source of inspiration.
Here's the quilt: