I have lived in the seattle area for 3 years and just made it to the falls with our last batch of visiting family. It is quite an engineering marvel! You can hear the roar of the falls before you leave the parking lot/can see it. The mist rises up from where the falls rush into the water and create amazing photo ops. The late spring/early summer are some of the best times to visit because the mountain snow is melting fast and it creates more impressive falls. Make sure you get the brochure that explains how the falls' engineering works. There is also a train museum with lots of old (most are not restored) trains and a restored depot. You can drive by and see all the trains, just a few miles down road from the falls.
Pros: no fee to see the falls, amazing photo ops
Cons: parking lots have tiny spots and are very full
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