The first unknown he encounters is not knowing how he will survive the fall into the water. He cannot see anything, however Rainsford uses his hearing to guide him towards ShipTrap Island.
Next, he knows there must be people on the island because he heard gun shots, but he wonders what kind of men they could be, especially considering the dark allure of the island. He solves this by deciding to follow the shoreline until he came to what he needed: footprints. He followed those until he arrived at the chateau and meets Zaroff.
His next unknown is figuring out how to survive the hunt. To solve this, he creates fake trails and a series of traps. This shows how skilled, intelligent, and resourceful he is, all characteristics which enable him to triumph in the face of the unknown.