As long as you want it to be. There are lots of trails and switchbacks
https://www.fmnp.org/trails.php This is the nature parks webpage. There is a trail map on this page as well as post mileage for each trail section.
As Lonnie stated, there are multitudes of trails within the Marquam Hill Nature Park. I completed the 1.8 mi Marquam-Flicker loop starting from Terwilliger.Blvd
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