Augustine, writing in the late 4th or early 5th century CE (De Genesi contra Manichaeos 1.(15).24) reports on people making an annual pilgrimage each summer up the fairly easy ascent to the St Antonios peak, to make sacrifices to Zeus at a shrine there. The shrine is also mentioned in Solinus 8.6; the site has been found, and archaeological evidence shows that it was still being visited through the 4th century.

There's an older thread on the subject here. I don't know everything there is to know about this subject, mind, and I don't have access to site reports on the shrine, so there may be more to say on the subject.

As one of my posts there explains, Augustine is echoing a passage in the Odyssey describing conditions at the summit. Though filtered through an understanding of how air works that is obviously wrong, the Odyssey passage does tend to suggest that people were strolling up there a millennium earlier too. I'll just copy-and-paste the extracts I quoted in the other thread:

There's a passage describing the summit of Olympos in Odyssey 6.42-46 that is very similar to Augustine's second-hand report of conditions there, which makes me suspect that the Homeric passage is not purely poetic imagination. The Augustine passage goes (tr. Teske):

That mountain of Macedonia, called Olympus, is said to be of such height that on its summit no wind is felt and no clouds gather. By its height it rises above all this moist air in which the birds fly, and thus birds, it is claimed, do not fly there. This is said to have been disclosed by those who climbed the peak of that renowned mountain each year for the sake of some sorts of sacrifices. They made some marks in the dust, and they found them intact the next year. This could not have happened if that place was exposed to wind or rain. Moreover, because the thinness of the air on that peak did not provide them with breath, they could not remain there without applying wet sponges to their nostrils from which they could draw the thicker and usual breath. These men also reported that they had never seen a bird in that place.

(Augustine repeats the story that no rain falls on Olympos in a few other places, and in one place he attributes it to "one of the pagan poets"; Teske suggests this could be Lucan Civil War 2.271, "Olympus towers above the clouds".)

The Odyssey passage goes (tr. Lattimore):

for Olympus, where they say the gods' abode is firm forever.
It is not shaken by winds or ever wet by rain,
and snow does not come near it, rather, cloudless clear air [aithrē]
spreads, and white sunlight plays, upon it.
In it the blessed gods take pleasure every day.

Both of these reflect the Greco-Roman idea that the lower atmosphere is dense, breathable aēr that is moist like fog and obstructs vision; above that is the aithēr, which is clear, bright, and fiery. The thinner atmosphere on mountain-tops is evidently getting out of the aēr: this is why people use moist cloths as a breathing aid(!) in Augustine's description. (Notice that Lattimore's translation confuses the two.)

And yes, this does seem a more likely source for Augustine's statement about rain never falling on the summit.