As we head up for the summer solstice, it is worth pointing out that one of the 15 Neolithic barrows at Carrowkeel, Sligo in Ireland has a lightbox which is aligned to illuminate the tomb at summer solstice sunset. This is found at barrow G, I have added some photos of the entrance to the tomb, (which is a tight fit), the blocking stone is covered in cup marks to the rear. A lightbox lets light into the chamber at certain times of the year. The most well-known example of this is found at Newgrange, Ireland, which illuminates a long corridor to the end chamber on the winter solstice sunrise. This lightbox would work in a similar way, it has also been suggested that the alignment could also work for the full moon nearest the mid-winter solstice.
There is so much to discover at Carrowkeel, it is well worth the climb to the top of the hill. At tomb G at Carrowkeel, there is also a large basin stone to the right of the entrance which is covered in cup marks. It’s well worth the climb inside as there is a wonderful keystone in the roof, the interior shows what an amazing engineering job was made on building the tomb. A virtual tour of the tomb is available here and lets you look inside this tomb and at a number of other in the complex.
A few pictures of the Carrowkeel tombs and the lightbox with cup marks.