Kevin and I spelunked in the J4 cave today. It was more treacherous than usual because of the 2 or 3 inches of snow on the ground outside the cave. This made it pretty hard to climb up the rockface the 40 or 50 feet to the pipe which is the cave's entrance. It was about 20°F outside, but inside the cave it was a toasty 50°F. We spent 3 hours inside and made it to the first mud room, our progress greatly hindered by our incessant photography. I'd been in J4 four times before, but I was never brave (dumb?) enough to take my camera, until today.
DISCLAIMER: sorry about all the photos of Kev's backside. He went first, and you can't exactly stop and turn around in the middle of the crazy maneuvers you need to do in J4, so you'll just have to deal with it.