The legend of Titicaca is that people lived happily in its valley, where the land was extremely fertile.
The gods of the mountains, the Apus, protected humans and prohibited only one thing: they could not climb to the top of the mountains, where the sacred fire was burning.
But the devil also lived in those lands and it was unbearable for him to see all that happiness. So he incited the men to go up to the top of the mountains. Los Apus' fury was so great that he released Cougars who devoured the whole population, except for a couple.
Given this carnage, the Sun God, Inti, wept for 40 days and 40 nights, thus forming Lake Titicaca. When the sun returned, the couple, who had fled in a boat, saw that the Cougars had all turned to stone.
This is probably the etymology of the name of the lake. Titi, which means cat or puma, and kaka, stone.