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In Speleophilately International Nr45, David Brison in his column on "stamps in need of field checks" mentioned this stamp on which "at the base of the cliff the engraving shows what appears to be a huge marine cave entrance". But no report could confirm this point.

After reading David's lines, I published a photocopy of the stamp and a brief note in La Lettre du Spéléo-club de Paris, 130, december 1994, asking for information [every issue of this short monthly newsletter is illustrated by a different caving stamp]. A few days later, I received a letter from a friend living in Nice, Eric Gilli, a caver and geologist, who confirmed that the black spot at the foot of the cliff was not an "illusory cave", but a large sea cave. In 1980, he explored the cave in the company of Jean-Pierre Mairetet*, using Jean-Pierre's sailboat, an old Turkish caique. A survey was made and published in Spéléologie, 109, oct-dec. 1980, the bulletin of Club Martel, Club alpin français, Nice, together with a short humorous report by Eric Gilli :

"The boat is anchored at Cape Sounion, at the foot of the majestic temple of Poseidon. But this black hole at sea level, isn't that a cave? We donned our diving suits and went to explore the cave under the stare of clusters of tourists haunting these places. Although the cave is located in a metamorphic zone [gneiss], the reader can see that it has no cause to be jealous of limestone caves. It has a vertical pit, two rooms, two entrances and a sump. We dived the sump without any scuba equipment, thus giving proof, if this were necessary, of the high level of French Speleology."

* Jean-Pierre Mairetet (1941-1988) was a member of Speleo-club de Cannes and Speleo-club de Paris. Under Michel Siffre's supervision, he made a six-month "Beyond Time" experiment in Aven Olivier, a cave in the French Maritime Alps. He was a great collector of caving books and had one of the richest caving libraries in ancient French underground literature (XVIIth or even before). He died in a skydiving accident.