Start at the beginning of the Centennial Trail, just past the front gates of the park. Follow the Centennial Trail in its entirety, which brings you to the visitor centre parking lot. From here, just head to the road and go all the way to the most southern point in all of Canada. The Tip! Go as far as you can without getting your feet wet, take a picture and then take the same way back to the start.  About 20km, basically flat.

https://www.pc.gc.ca/en/pn-np/on/pelee/visit/cartes-maps
 

The Veischede Sun Trail offers the finest hiking fun on 38 kilometres (1192 vertical meters). It can easily be divided into two stages with overnight stay. Hikers can enjoy not only fantastic forests and magnificent panoramas, but also the Bilstein Castle (today a youth hostel) and the "Hohe Bracht" observation tower.

A ~70km loop in the Sawtooth Mountains near Stanley, submitted by Garrick Arends:

Starts at the northenmost part of the Rock Creek Trail in Olney Maryland, the address is roughly 19801-19813 Muncaster Rd, Derwood, MD 20855 (39.182411, -77.113771). This will follow the Rock Creek Trail system all of the way south until we hit the DC line at (38.986208, -77.053093). When you hit the DC line we follow the NPS's Western Ridge Trail in Rock Creek Park until Bluff Bridge at (38.936740, -77.048038) where the trail turns into Rock Creek Trail.

A 65km beach run (not on the highway) on the west coast of Nambia.  End points are the De Duine Hotel in Hentiesbaai and the  Strand Hotel (beach hotel) in Swakopmund.