Some kind of alien presence he believed was consuming other worlds and would someday come for...
Seg: This fortress. It's why they killed grandfather, isn't it?
Charys: Val was determined to prove we weren't alone in the universe. After the council shut down his work, he would come here to work in secret.
Seg: He found something he wasn't supposed to.
Charys: Some kind of alien presence he believed was consuming other worlds and would someday come for Krypton. He tried to warn the Council, and they silenced him for it. Your father and I believed him. There was nothing we could do. With Val dead, we didn't even know how to get in this place. Your grandfather was no traitor. He was a hero. He was trying to protect Krypton. He believed in it so much, he was willing to do for it. We have to finish his work. Together.