Monday marks the 28th anniversary of the Great Chicago Flood.
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On April 13, 1992, nearly 250 million gallons of water rushed into the Loop's underground system after a construction crew accidentally breached an old freight train tunnel.
The flood forced packed streets to be evacuated and gave people a rarely seen look at the underbelly of the city.
The leak even flooded the Kennedy Expressway at Hubbard's cave before crews were able to stop the water flow.
Engineers were finally able to figure out how to seal off the tunnel on both sides of the river, stopping the flood but leaving one big mess.
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It's estimated the flood cost the city nearly $2 billion between clean-up costs and lost business.
Later, it was discovered that the city was told of the fragile tunnel before it collapsed.
The remaining tunnels are still beneath the streets, holding power lines and communications wiring.