At Blidworth in a hollow to the west of the village are some masses of Bunter conglomerate, which stand out above the level of the fields. They remind us of the Hemlock Stone, and like it, are connected by tradition with the pre-Roman past, under the name of Druid Stones. The largest of them rests upon a knob of rock which juts a little above the soil; it has been hollowed from the western side for a distance of about six feet into the interior of the mass. The hollow is pierced through the back in such a way that, it is said, the aperture exactly faces the sun on the morning of Midsummer Day. Thus we are again pointed, as in the Beltane usage on Stapleford Hill*, to rites in which reverence for the sun played a leading part.
*ie the location of the Hemlock Stone.
From 'The Victoria History of the County of Nottingham' v1 (1906), edited by William Page.
In addition to a nice photo, Dr Millington's article mentions something that's suggested in the Victoria County History - about various other holed stones being useful to pass your ill children through to perk them up. But maybe he's got a lead - a local lane is called Ricket Lane... so maybe the hole was used to cure rickets? You never know.