While I searched if the pilgrims that went to Skellig Michael visited also Mont St. Michel and Sacra di San Michele, I found an amazing information about a book. I quote the presentation of this book.
The St Michael-Apollo Axis, a Study in Sacred Geography, by Lucien Richer, translated by Francesca Greene
The Apollo line is so named because the solar deity, in its active form, was Apollo in Greece. Richer's brother Jean had discovered that Greece was geographically many overlays of zodiacal patterns, with angles of 30 degrees spreading from oracular centres. After a dream involving Apollo, Jean could understand that the birthplace of Apollo, Delos, Athens, and Delphi were aligned at 30 degrees north of west. It fell to Lusien to extend this alignment out in both directions, to north west Europe and to Jerusalem.
The Michael-Apollo Line passes from northeast to southwest through :
St. Michael's chapel on Carn Brea in Cornwall,
St. Michael's Mount in Cornwall,
Mont St. Michel in Brittany,
Sacra di San Michele in Piedmont,
San Michele at Castiglione di Garfagna,
Monte Sant' Angelo, Monte Gargano, the site of the first recorded appearance of the Archangel Michael.
Mount Carmel in the Holy Land.
The history and geodetic character of the line are explored in this terse and pithy piece of writing. Important subjects such as the Gargan giant motif for the earth energy, the significance of islands and peaks and brief exploration of the "itinerary" of the line make this an essential complement to a rare corpus including Dance of the Dragon.
Amazing, isn’t it?
Four main Saint Michel’s Sanctuary standing on top of sharp rocks, “midway between earth and god”. They are and easily accessed, stand on an almost straight line and are almost equidistant. From North to South :
Skellig Michael, in south western Ireland,
Mont Saint Michel in Normandie (France),
Sacra di San Michele in Piémont (Italy)
Santuario di Monte San Michele on Mount Gargan in Puglie (Italy).
Is that pure chance or is it on purpose? I don’t know
The three latter are undoubtedly linked as for centuries, pilgrims used to go from Mont Saint Michel to the Gargano, passing in Piedmont, at Sacra di San Michele. It is dubious that they included in their trip the pilgrimage to the Skellig, but who knows!
In 2007, The Saint Michael’s Ways was formally awarded certification as a “Cultural Route of the Council of Europe”. It lists the The St Michael sites as follows :
Monte Gargano, in southern Italy; the Sacra di San Michele, on the edge of the Alps, in Val di Susa between Mont Cenis pass and Turin; St Michael's Mount in Cornwall, a county of south-western England which contains "Land's End" and is a place of legend and Celtic monuments; the chapel of Saint-Michel d’Aiguilhe, in its spectacular position on volcanic rock above a suburb of Le Puy-en-Velay; Saint-Michel de Cuxà, in the Canigou massif; the Skellig Islands in Ireland, where Skellig Michael, a steep rocky island, was for several centuries home to hermits devoted to the Archangel; Brussels named its cathedral after Saint Michel, the city’s patron saint, who is closely linked to the city's history and origins.
This is what I wrote before I found an amazing piece of information (next tip).
I have also a page on Sacra di San Michele and on Mont Saint Michel (currently building).