Diablo Lake Tour
Another 'must do' is the pull out to witness the turquoise beauty of Ross and Diablo lakes. The color is the result of glacial silt that gets scrubbed from the surrounding mountains and deposited into the backwaters of two massive hydroelectic dams.
One way to enjoy these are by taking a boat tour up the lake. Departing from near the North Cascades Environmental Learning Center (where you can also purchase tickets), these tours are equal part entertaining and informative.
Top it off with a tour of the powerhouse in Newhalem, a 'company' town owned by Seattle City Light. Besides the obvious tours, there is hiking aplenty in this area. Ask at the Learning Center for trail maps and information.