They go to a place called The Half- Blood, it's special because, only god's son's or daughter can go in there. Since, Percy was half mortal and half immortal can he was son of Poseidon, he was able to go in and so was Grover, but his mom couldn't.
Percy and his mother go to a beach house in the Montauk shores. This place is special for two reasons: first, is it where Sally met the god Poseidon and fell in love, and second, they have been going together to that beach on holiday ever since. Sally and Percy have a very strong relationship and it is then when they have to run away to camp-half blood after Grover finds them. In a way, that trip is the beginning of their adventure.
