Though it's possible to view the Mendenhall Glacier from outside the Visitors Center, the curved wall/window of glass allows a climate-controlled and unparalleled view. The cost of admission to the center is pretty cheap (and free during off-peak season). I would suggest making a stop here to help understand what you're looking at; although the view outside is breathtaking as well, there's not much interpretation unless there's you've got a guide.
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