Sunset viewed through the roofbox from inside Cairn G in Carrowkeel
The Summer Solstice this year in the Northern Hemisphere is on June 21st at 11:28 UT/GMT.
In the West of Ireland the Summer Solstice Sunset shines through the roofbox at Carrowkeel Cairn G, illuminating the chamber within.
This is much like the Winter Solstice phenomena at Newgrange and Maeshowe, and the Equinox Illumination at Loughcrew.
Thanks to Michael Fox of knowth.com for the photos.