America's Stonehenge, 5 mi. e. of I-93 exit 3 on SR 111, then 1 mi. s. to 105 Haverhill Rd., encompasses prehistoric stone structures proven by carbon dating to form the oldest known megalithic site on this continent. Continuing research indicates the site may be 4,000 years old; inscriptions deciphered offer possible evidence that Celt-Iberians used this site from about 800 to 300 B.C. Inscriptions are displayed and reading material is available as well a mobile app with an audio tour. Five alpacas are on the premises.