Instructions
Enter cabin three, which is unlocked. Look for a small shiny object on the ground -- this is the key to cabin one.
Visit cabin one and loot the shiny objects you find. One will be a key to another cabin.
Open the cabin door that corresponds to the key you have just found and explore that room for even more keys.
Repeat this process until all of the rooms have been unlocked. All five keys are hidden somewhere in the six cabins.