Lock 31 is the stone remains of a numbered lock on the Ohio & Erie Canal, beside the Towpath Trail between Boston and Peninsula. It is a quick history stop if you are already walking this stretch, rather than a destination that needs a separate trip. The usual approach is south from Boston Trailhead; the lock is about 1.5 miles south of Boston and one mile north of Peninsula.
NPS lists historical interpretation, an audio description and wheelchair accessibility here, but its page does not explain which surfaces along the approach meet that standard. It also notes accessible parking at Boston Store Trailhead.