In many cultures the solar god figure was interred, hung from the tree (think Odin/Woden, and also the Hanged Man of the Tarot), or dismembered like Osiris, for three days and nights at this midwinter time, to be born again, as the sun seems to be after this time of the shortest day, towards a gradual lengthening of daylight, once the sun moves on. (It's no coincidence that Jesus' birthday is close to the winter solstice.)
In West Cornwall, there are some enigmatic underground chambers called 'fogous'. Many stretch for quite some metres, and many have little round side-chambers known as 'creep' chambers. They're Iron Age in origin, and we don't know what they were built for.
Some suggest that they had ritual significance, and this seems likely. Other barrows have similar side-chambers (for instance in Brittany), and the thinking is that an initiate would be entombed, alive, in this little womb-like chamber for three days and three nights, to be 'reborn' at the midwinter sunrise (usually; sometimes solstice sunset) when the entrance was unblocked. This sensory deprivation would have either killed through shock, made mad ditto, or transformed the individual.
Until the house was sold some years ago now I used to lead residential workshops at a place called Rosemerryn, near Lamorna Cove in West Cornwall. The house was built within a double concentric earthwork dating from the Iron Age, and it has a magnificent fogou in the grounds close by. Just up the road is the Merry Maidens, or Dawns Men ('stone dance') stone circle dating probably from the early Bronze Age, opposite a pair of tall menhirs known as the Boleigh Pipers. Close by is another menhir, the Fiddler. (West Cornwall has a very dense concentration of prehistoric monuments.)
Sometimes we entered the dark throat of the fogou, and lit candles to float in the deep puddle caused by the collapse of part of the roof – a magical experience, and in itself gently transformative.
Meantime here are two poems written after entering the Boleigh Fogou a few years ago. They both appear (the second in a slightly different format, a prose poem like the first, below) in my collection Bardo – an appropriate title for this liminal time.