You live on a ship. All people do. no one ever left the ship. To dangerous out there. The ai on the ship decided to keep them safe an not open to outside unless missions. 
World where it's a death world. , nasty viruses. To large plants that eat, turn you mad, to fuguses. From bugs, that massive hives attack them. Many parasites, from worms in your skin, to brain bugs. Animals of all types. The smart creatures, large, scales, strong. Tribes of these large aliens live in underground cities. Some 