The Opera House at Boothbay Harbor, 86 Townsend Avenue, will offer a free class in the design and construction of gingerbread structures at 2:30 p.m. Wednesday, November 20, in anticipation of the Opera House’s annual Gingerbread Spectacular to be held December 13 to 15. Experienced builder Kevin Kiley will present time-tested recipes for strong walls and roofs, sure-to-set icing tricks and design ideas. People of all ages and skill levels are encouraged to attend; children under age 12 must be accompanied by an adult. Those who wish to participate are asked to register by calling 633-5159. Those interested in submitting an entry for Gingerbread Spectacular may call or visit the Opera House; registration forms are available at the box office.