The Sammamish River and Burke-Gilman Trails are well-trodden mixed use pedestrian trails that link Lake Sammamish to Lake Washington. This section is paved and mostly flat. Go as far as you like, with a 50 minute turnaround time. The linked map shows turnaround waypoints for round trip distances between 8.0 and 13.4 miles, but go as far or near as you like and turn back 50 minutes after starting.
Meet at Wilmot Gateway Park in Woodinville and run towards Lake Washington.
Google map at https://maps.google.com/maps/ms?msa=0&msid=210902867501053216022.0004dc9ca66de5135e1d8&ie=UTF8&t=m&z=13&vpsrc=1
Hope to see you out there!