| Pozzo del Merro | |
| Coordinates: | 42.0393°N 12.6805°W |
Pozzo del Merro is a flooded sinkhole in the countryside northeast of Rome, Italy. Situated at the bottom of an 80 m conical pit, at 392m (1,286feet) it is the second deepest underwater vertical cave in the world. In 2000 two ROVs were sent to explore its depths; the first, the "Mercurio (Mercury)" reached its maximum operative depth of 210m (690feet) without reaching the bottom. The second ROV, "Hyball 300", reached 310m (1,020feet) without touching down either.[1] A third dive in 2002 with the more advanced "Prometeo" robot reached the bottom at 392m (1,286feet), but discovered a narrow passage continuing horizontally.
The sinkhole, similar to the Zacatón cenote, was formed by volcanic activity eroding the carbonate rock.[2]