In chapter 5 how does Percy know where he is?

In Chapter 5 of "The Lightning Thief," Percy realizes he is at Camp Half-Blood when he sees the camp's unique environment and the presence of other demigods. He recognizes the significance of the various mythological elements around him, such as the training grounds and the magical barriers. Additionally, his conversations with other campers and Chiron help clarify his identity and the purpose of the camp, confirming that he is among others like himself.