Once visitors reach the last viewing platform, they will descend the final stretch of the path to the ‘bedrock’ level, known as the West Chamber, which contains the foundations of the original World Trade Center. Here, the visitor will arrive at the third stage of his/her experience. At this lowest level of the museum and WTC complex, the original column bases and concrete footings that supported the twin towers are exposed in the floor slab of the museum, defining a clear outline of the former towers. A surviving retaining wall or the original WTC, known as the “slurry wall”, is exposed and serves as a backdrop for the 36-foot “Last Column” - the final piece of steel structure that was removed from Ground Zero, whose surfaces had been gradually covered with moving written testaments and photos during the rescue and recovery effort.