I've written about it some in the past but not with much detail: Juneau really is the best place I have ever been for running in the mountains. When most people talk about living close to trails they mean they have a couple nice trails a few miles away and then several more that they can drive to in an hour or less. In Juneau there is a nice trail about 5 blocks away from pretty much anywhere you are... and if you drive in any direction for 10 minutes you'll give yourself access to several (if not a dozen) other trails.
I live at sea level (or technically about 20 feet above sea level). 2 blocks from my condo there is a trail that climbs for about 2.5 miles to just over 3,300 feet. About a mile up this trail there is another trail that branches off and traverses along the 1,000 foot elevation for about 16 miles one way with several different access points that create options for loops of any distance between 3 and 30 miles.
I work about 3.5 miles from where I live. Within a few blocks of my work there are 2 different trails that then branch out into several options. You can go fairly long with a more gradual climb (around Juneau anything less than about 750 feet per mile is considered gradual), or you can climb trails that gain more than 1,500 feet per mile. If you hop on your bike and ride for 15 minutes in any of 3 different directions you will have access to about a half dozen other trails.
The real beauty of the trails around here though aren't the established trails themselves but rather the terrain you can access once you climb up onto the ridges that these trails lead to. The options are pretty much unlimited. The only limiting factor tends to be the weather. When the clouds are low it can be pretty miserable (and dangerous) to be up on these ridges. When the weather is good though one can't help but want to climb up to the mountain tops every day.
Today a group of 10 of us assembled under some decent weather to climb up Mt. Juneau (about 3,500 ft.) and follow the ridge back behind it for several miles until eventually dropping down into Granite Creek Basin and looping back around on the most popular trail in town, The Perseverance Trail. Of all the ridge traverses in Juneau this is likely the most travelled one. Partly because it's so close to town and also because it's a fairly mellow route with no scrambling and very little route finding difficulties. All told though it's a 14 mile loop with about 4,500 feet of total climbing and tends to take most strong runners 3-4 hours.
We had 3 high school runners with us today who had never done this route and 7 others ranging between 20 something on up to 70. An unlikely group of companions for sure, but that's the way the running community is here. So many different personalities/ages but when we get together for a run like this we all seem to be so similar for that 3 or 4 hours. It's great. Today's run was great. I just wish I could decide which mountain I'm going to climb up next...