Visitors to the Denver Art Museum’s renovated North Building will walk through a new main entrance on West 13th Avenue Parkway, take additional elevators up to spacious galleries and seventh-floor rooftop views, and find extra room for student activities and socializing — including a 50,000-square-foot, three-story welcome center with a restaurant, café and event hall. That vision, which has been laid out in recent months by museum officials, inched closer to reality Wednesday as museum trustees and Mayor Michael Hancock ceremonially broke ground on the $150 million project, touting it as a new era in Denver’s cultural history. But the lavish event, which included a pre-lunch mimosa toast, brass quintet and American Indian blessing, symbolized more than the start of the three-year renovation and construction, which is timed to finish in 2021 on the 50th anniversary of the castlelike, Gio Ponti-designed structure. AAron Ontiveroz, The Denver PostA group of drone pilots perform during the groundbreaking ceremony for the north addition to the Denver Art Museum on Wednesday, Jan.