This is the Jalhay black route of 40 km and 1100 m accent/decent. There are currently (March 2021) 10 similar routes listed in the ExtraTrail system, which are all referenced on fastestknowntime.com.
Link to Route: https://extratrail.com/en/trails-in-jalhay-3/#d
38.91 kms; 1,105 m elevation gain
This is the Spa black route of 32 km and 1100 m accent/decent. There are currently (March 2021) 10 similar routes listed in the ExtraTrail system, which are all referenced on fastestknowntime.com.
Link to Route: https://extratrail.com/en/spa-trail/#d
31.78 kms; 1,100 m elevation gain
This is the Theux black route of 37 km and 1100 m accent/decent. There are currently (March 2021) 10 similar routes listed in the ExtraTrail system, which are all referenced on fastestknowntime.com.
Link to Route: https://extratrail.com/en/trail-in-theux/#d
36.88 kms; 1,076 m elevation gain
This is the Stavelot black route of 40 km and 1,500 m accent/decent. There are currently (March 2021) 10 similar routes listed in the ExtraTrail system, which are all referenced on fastestknowntime.com.
Link to Route: https://extratrail.com/en/stavelot-trail/#d
40.48 kms; 1,575 m elevation gain
This is the Trois-Ponts black route of 37 km and 1,200 m accent/decent. There are currently (March 2020) 10 similar Routes listed in the ExtraTrail system, which are all referenced on fastestknowntime.com.
Link to Route: https://extratrail.com/en/trois-ponts-trails/#d
36.76 kms; 1,234 m elevation gain
This is the Malmedy black route of 39 km and 1100 m accent/decent. There are currently (March 2021) 10 similar routes listed in the ExtraTrail system, which are all referenced on fastestknowntime.com.
39 kms; 1,071 m elevation gain
Link to route: https://extratrail.com/en/malmedy-trails/#d
The Natchaug Trail is a 17.8 mile blue-blazed trail traversing the Goodwin and Natchaug State Forests and General Nathanial Lyon Memorial Park. The trail starts at Pine Acres Lake, passing Black Spruce Pond, Beaverdam Marsh Area, Still River, Bigelow Brook, and lots of forest on the way to its northern terminus at the junction with the Nipmuck Trail. If running one-way, you will need to do an extra ~0.6 miles along the Nipmuck to connect with Eastford Rd.
Dan Bates submitted this logical, 45 mile loop:
Going clockwise from the North Windham Road parking area, this loops links the Nipmuck Trail's East Branch (6.4 miles), followed by 15.9 miles on the Nipmuck Main Trail to its junction with the Natchaug Trail, followed by the Natchaug Trail in its entirety (17.8 miles), followed by 0.25 miles on Potter Road to reach the Airline Trail, which is followed for ~5.5 miles to an exit near Boulevard Road, followed by a ~0.7 mile road connection back to the parking on North Windham Road.