Hint #1: It is on an island.
40.2083°, 9.4847° "Su Suercone" karst sinkhole in the Supramonte mountains of Sardinia, Italy. The limestones are being described as:"Western Sardinia Succession": Carbonatic shelf deposits: dolostones and dolomitic limestones, bioclastic limestones, oolithic and oncoid limestones, cherty limestones, mudstones, marly limestones and marls (http://www.geo.tu-freiberg.de/palaeo/exkursionen/sardinien2010/sar_nord_low.jpg). The N-S trending valley is a dextral fault separating the limestones on the left to granodiorites on the right.I've been scanning over every limestone area and every island in the mediterranean exept Corsica and Sardinia. So I gave up. I did no look in Corsia/Sardinia as this is my favourite vacation island and I thought I would know every hole in the ground. So silly I am. I definetely have to improve my knowledge about Sardinia.
"The armpit" it is - Su Suercone. :)I was looking at karst regions, for once my searching was actually somewhat work related. When I came across this big round hole, I decided to mark it for a future WoGE. Over to you, Felix!
Woge 462 is at: http://woge-felix.blogspot.de/2014/11/where-on-google-earth-462.html