A short but taxing hike up to the incredible view at Portage Pass, and a continuation down to the lake if you're in the mood!
Probably one of the best bang-for-your buck hikes I've ever been on. Starting from the trailhead, which is just on the Whittier side of the Portage tunnel, you'll hike up 800ft in one mile on a mostly wide, rocky trail. In what seems like no time at all, you'll be at Portage Pass, with views of the Passage Canal in one direction, and the incredible vista of Portage Glacier, Byron Peak, and Carpathian Peak in the other. It is truly spectacular.
If you want to get a bit more hiking in, it's another mile down from the pass to Portage Lake. You'll pass Divide Lake on the way, and reach a beautiful glacial lake at the bottom. The lake has only become visible since approximately 1914, due to the retreating Portage Glacier.
Return the way you came (and be sure to time your hike with the tunnel, which is one-way and runs back towards Anchorage once every hour).