If you only do one thing in Juneau (and you have teens), you NEED to kayak the Mendenhall Glacier. You get a great guide, great views and great exercise that combine for a once-in-a-lifetime experience. This is probably the best way I can think of to get up close and personal with a glacier! Make sure to research proper clothing beforehand because the water isn't warm and it rained the entire time we were out on the water - still my favorite Alaska experience!