120,000 years ago, the Europe where Neanderthal humans lived was warm and fertile. Before the DISASTROUS ice ages befell the people, they could have easily evolved an advanced technological civilization and space travel. They had plenty of time to explore the solar system, find the moon of Saturn named Titan where there is water and a warmer more stable climate than earth. They had time to establish colonies and when the ice ages destroyed their civilization and pushed the remnant back into being cave dwellers, there was little reason to return to earth.
Homo sapiens managed to begin agriculture and advance to space travel in 8000 years. Neanderthal had more than enough time, and a bigger brain to make it easier. No wonder when they came back to earth as the TITANS, fathers of the gods they began to breed with the little people, the homo sapiens, to raise their abilities. Nowadays people in Europe and Asia have as much as 3.5% Neanderthal DNA. I and my family are Autists with only 2.5%.
5781 years ago these Titans came back to earth. They began a breeding program to improve Homo sapiens by mating with them giving rise to albino like humans with reddish hair. HTheir progeny built the Sumerian empire and as Phoenician traders explored the earth created the Silk Road, spread the trade lingo that became Indo-european languages and became rulers of the earth. I expect that the Breakaway Civilization of Neanderthals also has underground cities in the arctic and antarctic using advanced technology that can survive asteroid impacts. In other words they do not NEED the sunshine or the wild natural environment to support them. Likely they already have sent many generational starships to other star systems
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.quora.com/Is-it-possible-that-the-Titans-in-Greek-mythology-were-based-on-the-Neanderthals-since-they-were-seen-as-less-cultured-and-tribal-than-the-gods&ved=2ahUKEwjakO_427bwAhUPrZ4KHfQ7B1sQFnoECBwQAQ&usg=AOvVaw1jJcAqYUg8-DrrlpVcVhGY