Seattle up to ACA's Northern Tier route to Glacier National Park and then backtracking to the Great Parks North, Trans Am and Great Parks South, ending in Cortez, CO was nice. Mid-May might be a little early to ride the North Cascades Highway, but maybe not. Both times I crossed I left Seattle in late May, so I hit the climb around May 31/June 1. If you continue on to Durango you can fly out from there.