I'll add more categories:
Closest stretch of Interstate in either direction: Southbound lanes of I-95 near Exit 54 in MA, about 15 miles away (I have been on this segment northbound only)
Closest exit: Exit 3, Lowell Connector, about 12 miles away
Closest exit that I didn't turn around immediately afterwards: Exit 52, I-495 (due to detour, not missed exit)
Closest freeway of any type: US 1 in Newburyport (freeway for only 1 mile), about 15 miles away; if that doesn't count, MA 128 (section that is not I-95) east of Exit 18, about 25 miles away
Closest town not set foot in: Boxford, MA (closest point about 1 mile away as the crow flies; I have been through it, but never set foot)
Closest town never in at all: Pelham, NH, about 5 miles away
Closest 2di (closest 3di was mentioned in my first post here): I-95 (MA) south of Exit 20, about 30 miles away
Closest numbered state border crossing: NH 121A, about 10 miles away (there is no MA 121A), however, I have been really close to it
Closest year-round public transportation: Bus 01 on MVRTA, 0.6 miles away (I have been on a closer section)
Closest Interstate I have traveled none of: I-190
Closest US route I have traveled none of: US 1A in Maine closest to New Hampshire border
Closes state route I have traveled none of: NH 128 (I have traveled none of MA 108, but I consider MA/NH 108 one route)