For a multi day event the Ride Across Portugal is fantastic. Challenging riding, good roads, great scenery, low traffic , very high level of support.
http://rideacrossportugal.com/
Closer to home Hot Doggot in Madison County NC, just north of Asheville. I think it may be the best Gran Fond type ride in the Southeast, that no one’s ever heard of. Beautiful roads. Challenging climbs, and great support. While it’s essentially a Gran Fonda, as a timed event, they don’t call it one, and thus is much cheaper.
https://hotdoggett100.org