The great Mississippi flood of 1927 was essentially the Hurricane Katrina of the 1920s. After weeks of heavy rains caused multiple levees to fail, millions of acres flooded across seven states, killing as many as a thousand people and displacing half a million. The damage cost $1.3 trillion in today’s currency—about a third of the federal budget at the time. Congress and the Army Corps of Engineers vowed it would never happen again, but another flood devastated the region ten years later.

The problem? No one really understood how the Mississippi River worked.

As Dylan Thuras of Atlas Obscura explains in the video above, locals tended to erect measures that successfully prevented flooding in their communities but accidentally inundated other towns. The region needed a system-wide approach that would help engineers understand how the river and all of its tributaries worked together. In the days before computer modeling, the solution was relatively low-tech: Build a hydraulic scale model of the river basin, one that would allow engineers to watch how various water inputs affected the area as a whole. The result, according to Atlas Obscura, is the largest small-scale model ever built, or, as Thuras puts it, an “engineer’s Disneyland.”

The model encompassed more than 15,000 miles of rivers that make up the Mississippi basin, shrunk down into eight miles on about 200 acres of park land near Clinton, Mississippi. Since the project got going during World War II when labor power was scarce, the Army Corps used 3000 Italian and German prisoners of war as laborers.

It took more than 20 years to complete, but engineers and scientists ran close to 80 simulations on the model over the years, notably preventing a major flood in Omaha that could have caused as much as $65 million in damages.

Today, the model—donated by the Army Corps of Engineers to the city of Jackson, Mississippi, after computers replaced scale models in the 1970s—sits abandoned, a small-scale engineering feat turned piece of forlorn public sculpture. It is now a popular site for radio-controlled car hobbyists.

For more, watch the video above—and check out the entire Atlas Obscura 100 Wonders series of unusual places to visit.