Date: April 1 - April 30
Place: The Skagit Valley is 60 miles north of Seattle, Washington, 60 miles south of Vancouver, British Columbia.
Website: http://www.tulipfestival.org/index.php
Go there early. Two years ago, I went there early but by the time we left, the exit was packed with cars..
One day should be enough. I would suggest leave early to avoid traffic. For sure if you go there near noon, the whole i-5 near that area will be packed. It would be hard to even get off highway.