June 21, 2018 is the summer solstice this year, celebrated at Stonehenge and across the globe, for the longest day of the year. “Sol + stice derives from a combination of Latin words meaning “sun” + “to stand still.” As the days lengthen, the sun rises higher and higher until it seems to stand still in the sky.” http://www.chiff.com/a/summer-solstice.htm
Within Welsh mythology, there is very little discussion of the solstices or what holidays were celebrated within the celtic/druid year. This is not the case of Stonehenge, which archaeologists and historians have studied extensively.
“When one stands in the middle of Stonehenge and looks through the entrance of the avenue on the morning of the summer solstice, for example, the Sun will rise above the Heel Stone, which is set on the avenue. If one stands in the entrance and looks into the circle at dusk of that day, the Sun will set between a trilithon.”
There are a couple of stone circles in Wales (more than a couple, but many are ruinous and not properly documented). One, Bryn Cader Faner, is a small cairn 8,5m (28ft) wide and less than 1m (3ft) high, with fifteen thin slabs leaning out of the mass of the monument like a crown of thorns, near Porthmadog.
A second is Carn Llechart near Swansea. It “is one of the largest ring cairns in Wales. It is an unusual circle of 25 stones leaning slightly outwards and surrounding a central burial cist. Aubrey Burl in his “The Stone Circles of British Isles” wrote that such rings were thought to be the first stage of development of stone circles, but that these cairns, however, are almost certainly too late to provide such an ancestry. The reverse seems likely, that the existence of stone circles elsewhere impelled people to place tall stones around the bases of their own round cairns, a fusion of traditions resulting in monuments like spiky coronets. Such cairns may be seen on North and South Uist, and in Wales at Carn Llechart and Bryn Cader Faner. The circle is 12m (40ft) in diameter, and the central cist has its east side stone and capstone missing. It seems that there is no entry to the circle and no trace of covering mound. A possible date for the site is the 2nd millenium BC. In the area there are also a Neolithic burial chamber and some Bronze Age cairns.” (http://www.stonepages.com/wales/wales.html),
Archaeologists are of the opinion that these stone circles have more to do with burial sites than worship, giving them less kinship to Stonehenge than one might think at first. This site (http://www.geodrome.demon.co.uk/megalith/stone.htm), however, argues strongly for a similar rationale for stone circles in Wales, in which the author has documented the alignment of a number of stone circles.
When we were in Ireland in 2016, we found that many of the barrows, burials, and circles were oriented to the sun, either the winter and summer solstices or the spring equinox in particular.