You are one of several hundred colonists on a long term deep space mission to some far away star system, to save resources the entire crew has been placed in cryo storage for the duration of the voyage. At some point, for some unknown reason you awaken. You find that your cryo tube has been moved into a sealed room, as you shake off the effects of long term cryo you notice something odd seeping through the hatch at the other end of the room. When you open it you find that the passage way beyond is covered in some odd growth or creep, the air beyond your little compartment is damp and musty. The growths seem to grow and cover the interior hull with expanding veins and tumorous growths, at this point you have a choice to make, either try and find your way to a control room and find out whats going on, or hide in your compartment and hope someone finds you.
I'm basically picturing the ship having been invaded by an alien ecosystem, the ship itself would be massive, many miles long full of cramped corridors, large vent shafts (Aliens eat your heart out). To top it all off, thousands of colonists running around in the middle of it. I basically have a quite a few ideas, maybe the character stumbling about as the colonists do the same 'encountering' the alien organisms with interesting results. Probably everything from your xenomorph stylized creatures, grab or kill, the grabbed being implanted with more creatures. Even had this one interesting idea for a spider like creature that 'swallowed' its victims into the central part of it's body where it soaks them in odd fluids before expelling them out the back wrapped in a cocoon, possibly transformation going on. Maybe even full blown arachnids, webbing, oviposition. Its just such a wide area to cover, the possibility when rigging this as a group RP only makes things all the more interesting.