In 1985, a local man bought a dilapidated 200-year-old mansion in the San Telmo neighborhood with plans to rehab the property and open a restaurant. Now the place is called El Zanjon and is considered by some to be the most important archeological site in Argentina's capital and largest city.
That's because early in the project workers discovered a sizable brick tunnel extending across the neighborhood and intersecting with another tunnel. Matching the excavations with the 1800 city map showed two streams intersecting on this property. The tunnels offer a glimpse at early attempts at urban flood control taking the streams underground, solving a drainage problem, and creating more buildable land in the growing city.