Seattle, WA is a large seaport town in the Pacific Northwest of the United States. It is a great spot to recruit gutter trash for your very own sparklepire army for the purpose of killing a Mary Sue. It is also perfect for an excuse to your lame single father for not going to the prom as you whine incessantly about everything.
In the books, Bella seems to think that she can take a day trip from Forks to Seattle, driving there by way of Olympia and Tacoma. In reality, this is about a five-hour drive, not counting multiple stops for gas.
She seems unaware of both the Bainbridge Island Ferry and the Tacoma Narrows Bridge, either of which would save her about an hour and a half.
Whatever route you take, you cannot take a day trip from Forks to Seattle and expect to be home for dinner.