We would usually run directly from T1 to the river and back.

There's no need for shuttles or trains, as you enter the forest very close to the airport. Exit T1 on departures level, walk along the departures ramp east-wards past a DHL facility, cut diagonal through a parking lot that sometimes has busses towards a traffic light intersection which crosses an access road (look for a bus stop). This meets a walking/bike path, so continue eastwards until the pathway turns leftward and goes underneath two freeway bridges past a firestation, cross a ramp (there can be highspeed cars here in one lane), go under one more bridge (this is near some hotels, a DELL office, and a gas station), and you are in the forest!! From T1 doors, that is a bit more than 5 minutes. Now you can run all the way to the river on gravel paths along multiple routes. We've done this a bunch of times, always choosing a different point on the river to visit, therefore different routes -- a cellphone map is good enough. For the first while you have widebody takeoffs above you. It is never boring. There's ponds where people fish, parks with berries and apples, fields which change colour with the season, huts with roofs covered in moss, people cycling to/from their Airport job, and if you choose the right point on river you can grab a coffee before heading back.