Last week's answer

Question: Originally built in 1882 to haul coal across the Kinzua Creek valley in Pennsylvania, the historic Kinzua Viaduct stood 301 feet tall. In 2003, while engineers were actively restoring the bridge, a powerful F1 tornado struck the valley, collapsing 11 of the central steel towers. Rather than tearing down the remaining wreckage, how did park officials and structural engineers repurpose the surviving 600-foot section of the bridge?

Answer: They converted the standing portion into a high-altitude pedestrian Skywalk ending in a glass-bottom viewing platform directly over the collapsed debris.

The Pennsylvania Department of Conservation and Natural Resources submitted a proposal to construct an $8.9 million skywalk, after the tornado caused bridge construction to be out of reach. The skywalk was proposed to preserve tourism in the area. The pedestrian lookout used the bridge's remaining six towers, which were reinforced, and crews constructed a new bridge decking with installed new ramps and railings. 

Source: Pennsylvania Wilds