From Stefano Ruia:

Re: Probe to explore deepest known sinkhole (March 8): Zacaton cenote is not the deepest sink-hole in the world submerged by water. The “Merro Hole,” very close to Rome, Italy, is deeper: two years ago a ROV has reached 1, 300 feet and the bottom is still deeper. A geologist of University of Rome (Giorgio Caramanna) is working with collegues working in Zacaton on a scientific project. Just this month Jim Bowden (the explorer mentioned in your issue) is arrived in Italy to have a look at the Merro Hole.