We did a lot of awesome things while my family visited a few weeks ago, but I think my favorite was the Tracy Arm Fjord and Glacier Cruise. It's a full day of boating out to the fjord and glaciers, but definitely worth a trip if you have the time while you're in Juneau. We saw whales (my first orca!), seals, and tons of sea lions out on the iceburgs.
They take you out to North and South Sawyer Glaciers, inside the Tracy Arm Fjord. It is absolutely magical out there and I'm really hoping I can take another trip out there someday...
...we really lucked out, too. It was a pretty high chance of rain, and it's Juneau, but we had one of the most gorgeous days ever. It still would have been fun, and you have seats inside the boat so you wouldn't be drenched, but I loved getting on the top deck to view the wildlife and gorgeous landscapes.
Make sure to bring a jacket, it gets pretty chilly by the glaciers and if you go to the top deck while the boats going, that wind will get you!
More places to visit in Juneau here.