MIDDLEBURY — The Sheldon Museum presents Middlebury’s Historic Core, a walking tour of Middlebury led by Glenn Andres Sunday, July 14 and 21, at 2 p.m. The core of Middlebury Village preserves landmarks of state and national stature. It also speaks of much of the town’s colorful history from the 18th into the 20th centuries — booms and busts, strong personalities and rivalries, ambitious patrons and master builders, educators, lawyers, politicians and industrialists.