Juneau is the only US state capital you cannot drive to. The mountains behind it are too steep and the icefield above them too big, so everything arrives by boat or by air, which is also why the cruise dock is a hundred yards from the state legislature.
It is usually the longest port day of the week, and that is the whole point of it. A twelve-hour call is enough for a whale-watching boat and the glacier, which is the standard combination and is standard because it works.
Mendenhall is a drive-up glacier, thirteen miles from the dock, and that accessibility is the trade: it is busy. The walk to Nugget Falls is flat, paved and worth doing; the West Glacier Trail on the other side of the lake is a real hike and is nearly empty by comparison.
Whale watching here is about as reliable as it gets. Auke Bay operators generally guarantee a sighting between June and August and generally do not have to honor the guarantee. Boats are small, the water is sheltered, and the humpbacks are feeding rather than migrating.
Rain gear, not umbrellas. Juneau gets around five feet a year and the wind off the channel makes an umbrella useless.