I have in the past written about megalithic structures.
The idea I had was that, with the surfaces of the ice sheets uninhabitable, humans may have lived in warm caverns beneath the ice, building megalithic structures to hold up the ice..
Most megalithic structures are sited on high ground. so that water will drain away from them. Megaliths beneath melting ice would thus have been kept relatively dry.
The exposed overlying ice would have melted faster between megaliths, resulting in the formation of domes and barrel vaults, and ice capitals atop the megaliths which may well have resembled ionic and corinthian capitals. Greek and Roman architecture might well have origins in a deep subglacial past, recreated in a postglacial environment.
It would probably have been necessary to have raised floors above the streams of water on the ground surface.
Air temperatures in these subglacial chambers would have needed to be above freezing in order to melt the ice above. They may have been very warm.
If the ice was not deep, in daytime a pale blue light would have shone down through the ice.
With plentiful fresh water, mild temperatures, and light from above, the subglacial world would have been an ideal habitat for humans and other animals.
It’s usually thought that it took a colossal effort by thousands of people to raise these megalithic structures. But in a glacial world it may have been quite easy to slide large rocks over ice that had become a skating rink, and also relatively easy to drop such rocks into position. The megaliths were not raised.: they were lowered. They were quarried from hills above the ice surface, slid across it, and dropped into place.
This could explain why there are thousands of megalithic structures in Britain. They were quite easy to make.
It would also mean that the megaliths were built during the ice age, over 13,000 years ago, not after it. They are generally dated much younger because surrounding soils have carbon deposits of such ages. But the megaliths of the ice age would have had no such soils until the ice age ended and plants and animals began growing around them.
The biggest problem for humans would have been to find food in this barren glacial world. But if fish spawned in the warm glacial rivers beneath the ice, migrating as they still do today, humans might have had abundant food, much of which they could keep deep frozen in the ice around them, and cooked in hot springs. In addition there would have been other cave inhabitants, like bats and birds, to supplement their diet. There may have been all sorts of animals that found refuge in the caves beneath the ice.
Given a largely featureless ice sheet, navigation across it would have relied upon the sky. Humans would have needed to look up to find out where they were, following the sun and stars.