In the first book, Gone, Astrid goes home with Sam and Quinn to check if her parents are there. Starting directly from the marina to get to Astrid's house you would have to go up Brace Road and take the second turning on the left. The simplest route from there is to go right and then turn left, so you are in front of where you were anyway. Then you simply have to turn right assuming you were still facing the way you were going to go, continue to the end, and Astrid's house is on the left (diagram in all books near the back).