Compared to most of the forts, star- or otherwise, upon which I have trod, Fort Constitution is in pretty poor condition...granted,
NHStateParks.org describes what's there as the
"ruins of Fort Constitution." The fort sits on an active US Coast Guard base, which may or may not be a factor in its semi-decrepit state, but most certainly
does limit one's explorative possibilities.
But only in that one is unable to stroll all the way around the
outside of the fort...which I know because I tried, and was politely but firmly rebuffed. At the fort's miniscule parking area, there are signs instructing visitors to
remain on the blue line, a three-foot-wide trail leading to the fort.