You can find out more at the Exhumed Films website, click on upcoming shows to read about the marathon and there's a FAQ, to boot, in case anything leaves you scratching your head, eating whatever came off, and yelling "Nam land" at the top of your lungs.
In a nutshell: $20 to get in, you can bring a pillow and a blanket and sleep through a couple of films, leave and get some food and feel free to come back (with your intact hand stamp), bring your own food (just be neat and clean up after yourself), or go batshit and try to watch all 24 hours as if you were in the Eltingville Club. If you live nearby you can go home for a few winks and come back to catch a few more movies. If you live far away you can crash in the theater and pretend it's 1972, you're homeless, and you're stuck to your seat in a Times Square grindhouse -- only nobody's going to roll you or piss on you while you sleep. Cool!
I want to go and camp out and be stupid and have fun and watch crazy movies. I really do.