It's a 31x45 Fencing Match puzzle!
Longtime readers will no doubt be aware of my current tradition of posting a large 31x45 puzzle on every 25th puzzle. However, this first update of May 2010 represents a huge deviation from this tradition, because today, I give you, dear reader, three 31x45 giant puzzles. However, if these puzzles aren't your cup of tea, rest assured that I will resume posting more manageable-sized puzzles and puzzles in which you do something besides draw a loop soon enough. :)
ERRATUM: Well, my streak of over 200 puzzles without an erratum had to end sometime. This giant puzzle had one itty-bitty mistake that led to there being multiple solutions, as Kenneth Levine pointed out to me. The version below fixes this. I'm dreadfully sorry.