Although you wouldn't think of rainforests in Alaska, it does rain in Juneau a lot so I suppose it is not surprising that you would find 'Rainforest Trail'. There's actually couple of trails that go through the rainforest, both near each other close to end of the road in North Douglas. One is the Outer Point loop trail, a 2 mile boardwalk loop. The Rainforest Trail is a sprawl of intertwining trails, but a circuit is probably only about a mile. Both provide beach access. At high tide, the water comes gets very close to the forest. At low tide, you can walk to a tiny island (Shaman Island) across the way. I've seen people camp near the beach also.
The Outer Point loop provides a boardwalk for the trail users. The new Rainfores Trail, however, has a turnpike that allows users to look around the surroundings instead of worrying about falling off the trail. There is an article in the Juneau Empire that gives a little history about these trails:
http://www.juneauempire.com/visit/hiking/outerpoint.shtml.
