NASA-funded robotic sub finds bottom of world's deepest sinkhole

Carnegie Mellon researchers use sonar to map, demystify El Zacatón
A robotic vehicle designed for underwater exploration plunged repeatedly into the depths of Mexico’s mysterious El Zacatón sinkhole in late May, finding its previously undiscovered bottom 318 meters below the surface and generating a sonar map of its inner dimensions. The vehicle employed autonomous navigation and mapping systems developed by Carnegie Mellon University’s Robotics Institute.