One for fans of rock-art folklore. The stone's Canmore record isn't sure that all the cupmarks are man-made, but it's willing to go for 'at least four'.
In the district of Breadalbane, Perthshire - which has in it the Pool of St Fillans, famous for its supposed power of curing mentally afflicted persons - there are two boulders with water-filled cavities, which have a local reputation for their healing virtues. One is at Fernan, situated on the north side of Loch Tay, about three miles from Kenmore. It is a large rough stone with an irregular outline, somewhat like a rude chair, in the middle of a field immediately below the farmhouse of Mr Campbell, Borland. The rest of the field is ploughed; but the spot on which it stands is carefully preserved as an oasis amid the furrows. The material of which it is composed is a coarse clay slate; and the stone has evidently been a boulder transported to the spot from a considerable distance.
In the centre on one side there is a deep square cavity capable of holding about two quarts of water. I found it nearly full, although the weather had been unusually dry for several weeks previously. There were some clods of earth around it, and a few small stones and a quantity of rubbish in the cavity itself, which defiled the water. This I carefully scooped out, and found the cavity showing unmistakeable evidence of being artificial. On the upper surface of the stone I also discovered seven faint cup-marks, very much weather-worn; two of them associated together in a singular manner, and forming a figure like the eyes of a pair of spectacles.
The boulder goes in the locality by the name of Clach-na-Cruich, or the Stone of the Measles; and the rain-water contained in its cavity, when drunk by the patient, was supposed to be a sovereign remedy for that disease. At one time it had a wide reputation, and persons afflicted with the disease came from all parts of the district to drink its water. Indeed, there are many persons still alive who were taken in their youth, when suffering from this infantile disease, to the stone at Fernan; and I have met a man not much past forty, who remembers distinctly having drunk the water in the cavity when suffering from measles.
It is is only within the lifetime of the present generation that the Clach-na-Cruich has fallen into disuetude. I am not sure, indeed, whether any one has resorted to it within the last thirty years. Its neglected state would seem to indicate that all faith in it had for many years been abandoned.
From 'Notice of two boulders having rain-filled cavities...' by H Macmillan, in the Proceedings of the Society of Antiquaries of Scotland, v18 (1883-4), which you can read at the ADS website.