Add another vote for the Acadia National Park carriage roads. Over 50 miles of crushed gravel, car-free, well-maintained roads through around lakes, through forests, and wonderful views of coastal Maine. Some flat, some hilly, but nothing steeper than what horses can pull a carriage up and down. I'm honestly surprised that there aren't pro running groups flocking to the area during the nice-weather months.
Pilar, New Mexico, at the southern entrance to the Rio Grande Gorge State park back in late 70's...no traffic, cool clear air, quiet, and awesome scenery of the gorge walls. Never forget that...!
Rockefeller State Park Preserve and Old Croton Aqueduct Trail just north of NYC. Best running close to NYC.
My ex lived in South of Spain in the mountains of Malaga. Miss those beautiful hills, sunshine, blue skies, super smooth roads and valleys. Running past orange trees and mango trees the smell was so good. I was running 160 miles a week up those hills weekly elevation over 7000m climbing. I miss those days she used to drive along side me filming before we met up to walk some neglected dogs owned by this farmer.