Final answer:
Grover, Percy, and Mrs. Jackson are on their way to a hidden camp for demigods to seek refuge and training.
Step-by-step explanation:
Grover, Percy, and Mrs. Jackson are headed to a hidden camp for demigods when they leave the cabin in the middle of the storm.
This camp is a place of safety and training for individuals like Percy, who are part god and part human. It is a place unlike anything they've seen before, indicative of a world where mythological creatures and gods interact with modern life.