Although it is one of the world's biggest cave chambers, the Majis Al Jinn in Oman is just two metres wide at the surface.
A simple hole in the Selma Plateau, 100km south-east of Muscat, the unpreposessing aperture offers enthusiastic spelunkers a magnificent opportunity: an open subterranean chamber of four million cubic metres.
In addition to tempting "cavers", the Majlis has also tempted over the years many people looking for a way to get rid of rubbish. So the Dubai-based Middle East Caving Expeditionary Team was able recently to combine pleasure and public service: in a day of effort, The National reports today, 17 adventurers hauled some 80 kilos of rubbish from the cave floor up to the surface for proper disposal.
Much of the detritus down there was, one member of the team noted, lightweight material such as plastic bags that may have been blown into the cave, rather than being tossed in on purpose.
But the image of garbage blowing across the remote plateau is perhaps worse than the thought of deliberate dumping: if such a splendid site is so littered with junk we've thrown away, then no place is safe.
The environmental movement has a saying "There is no 'away'" which makes the point elegantly. Is rubbish really the one inevitable sign of human presence upon - and under - the earth?