There are several places to swim along here, including the popular Upper Ammonoosuc Falls. There are chutes and pools at the bottom of these falls that are safe to swim in at lower water levels, usually in later summer. Do not attempt to swim at the base of the falls during high water levels when currents can be very strong here. First timer's should observe others first. I'd never go there unless there were several others around.
Litter can be a problem sometimes.
Sometimes posted, sometimes not. An error would probably be fatal. None at site. Camp nearby off RT 302 at Zealand Recreation Area in National Forest. Follow the directions toward the Railway, turning north here onto Base Rd.