Anchorage has some of the nicest city trails in the world and the Tony Knowles Coastal Trail is its crown jewel. While I'm counting this as a hike, I recommend renting a bike for this.
Most of the trail is around Cook Inlet as well as marsh, muskeg, and spruce forest connecting Westchester Lagoon, Earthquake Park, Point Woronzof, and Kincaid Park. There are great views of Sleeping Lady (Mt. Susitna), Fire Island, and on clear days, Denali.
I am not kidding you when I tell you I've seen more wildlife on this trail than in the backcountry including red fox, coyote, moose galore, bald eagles and countless waterfowl. If you're lucky, you may see whales at Point Woronzof.
If you have a day in town between adventures, rent a bike and do it. You won't be sorry.
Warning! It is highly likely that you will encounter moose on the trail (and I mean ON the trail). Be careful riding fast when you can't see far ahead of you. If a moose is off to the side you can usually pass without impunity, but don't linger. If you see a cow with her calves, use extreme caution! When in doubt, turn back. Go to my Education page for more info on these big guys.
Warning! Under no circumstances should you ever walk onto a mudflat. It is very similar to quicksand and you will find it very hard to remove your feet from the mud. With one of the fastest tides in the world, you're looking at a deadly combination.
Even though this is a city trail, there are no stores or vendors along the way. Make sure you bring a water bottle and some snacks if necessary. At the end of the trail is Kincaid Park where you will find a community center open until 10 pm with restrooms and vending machines.
You can rent bicycles from many places downtown and midtown. There's a great shop at 4th and D in the Ship Creek Plaza.
Someday this trail will go all the way to Portage Valley. Until then, there is also great biking on the Seward Highway along Turnagain Arm.