I have been very fortunate to do some truly wonderful rides, from CA to DC (35 years ago, fully loaded) to the Big Sur coast (a couple weeks ago, fully supported).

If the opportunity arises, I'd love to try Alpe d'Huez and especially Mont Ventoux. With my current ability and attitude ("I go slow, but I make up for it by stopping a lot"), both would be all-day epics. I'd also love to ride up to the Madonna del Ghilsallo chapel and museum at Lake Como, which would likely also be an all-day epic.