I think it's the journey (or adventure) to a destination. All my long trips have a destination or area of the country I want to get too, but no other parameters. I know when I'm leaving and when I need to be back but have no set mileage per day, no hotel/motel reservations, I stop at, or detour to, anything that looks interesting. It's the only way to enjoy the trip IMO.
Most of the time for me, it's the journey. I ride about 90% of the time to work, 20 miles.... the only tune I can hear is AC/DC "I'm on the Highway to Hell"!!!
Then, there are "the rides" where it's both... the journey and the destination.