The hub of live theater in the region, the Bangor Opera House is celebrating its 90th birthday this Memorial Day weekend. The Art Deco/Egyptian Revival style building has staged numerous shows over the years, though none of them have been operas. The Opera House was gifted to the Penobscot Theatre Company in 1997, and since then, numerous repairs and restoration projects have kept the curtains opening show after show. As part of the birthday celebration, a cake has been made in the shape of the theater to be served during tonight’s opening of “The Underpants,” a play adapted by actor Steve Martin. Still shining on Main Street, officials hope the last remaining theatre in downtown Bangor will continue to stand for another 90 years.