Drive four hours east to Spokane’s Riverfront Park, where you can explore America’s largest urban waterfall via a soaring gondola ride. Kids can spin on the park’s 100-year-old carousel or scoot along the new Skate Ribbon. Make a weekend of it and camp at nearby Riverside State Park.
Here's the website of tourist clearinghouse Visit Spokane.
Note: Riverfront Park is undergoing a massive $70 million redevelopment; watch for new features opening throughout the summer and fall.
Related: More travel ideas and resources for Seattle-area families.