The Underground is the name for the renovated Conncourse, the three-quarter-mile tunnel system that links 16 blocks in downtown Oklahoma City. The original tunnel was dug in 1931, but most of the system was developed and became vibrant during the oil boom in the 1970s. And with the renovations completed in 2006, the Oklahoma City Underground once again is a vital part of downtown with its emphasis on art. The Invited Artists Gallery in the Underground, sitting underneath the intersection of Robinson and Robert S Kerr, features free shows created by Oklahoma artists. In addition, the tunnel system features a display of historic photographs of Oklahoma City.