Giants have been prominent in my game recently, which is somewhat surprising as they're mostly extinct. The characters came across a random giant, and killed it in a battle. The giant was carrying a mysterious stone cube with ancient carvings on it. This sparked the interest of the group's warlock, who then wanted to learn more about the giants and their bygone civilisation. The characters explored some giant ruins, encountered some undead giants, and finally managed to activate the stone cube, which was a memory stone. It allowed them to make sort of a vision quest to the ancient past, to the last days of the giant empire.
The giants of Artra are an ancient and primordial people. Aeons ago, when all the world was very young, they built the first civilisation. There are no different subspecies, they're all just giants. Colossal hairless creatures with thick pale skin on which there are patterns that seem like they were carved on stone. They are psionic and in their height, they mastered many kinds of magic, conquering death by finding a method to reincarnate with their memories intact. This and their psionic ability to share information allowed them to amass an incredible amount of knowledge. They used this to build a mighty empire, and bend spirits and dragons to their will. However, the inability to forget started to drive them mad. Some turned against their kin, longing for the oblivion of death that was denied to them. Some tried to maintain their sanity by crafting memory stones, artefacts that allowed them to expand their minds and better cope with the overwhelming amount of knowledge they had amassed. And some thought that the solution was to gather even more knowledge and power, and to this end they sought to take control of the last spirits that had eluded their colossal grasp: the gods. This did not end well for them, as the vengeful deities hurled a massive meteor at the heart of the giant empire. What happened after those last days is still shrouded in mystery. Some giants still remain, and the ruins of their ancient empire are still scattered across Artra, hiding their ancient relics and forgotten secrets. But the giants never recovered. The few who remain seem to wander the lands, their minds blank, some still carrying their ancient memory stones, the purpose of which they seem to have forgotten.
During the vision quest the characters managed to meet some of the ancient giants, in various states of madness. They also learned of a vault inside of a mountain, which some of the more sane giants had constructed to escape the wrath of the gods. Next they're heading there to see whether anything of it still remains.