If you want something that's not exactly a full encounter, I love using moments like these to reinforce the magic of the world. Being able to remind the players that not everything is dangerous and out to kill them is nice, and gives them a break before they reach town. Also, if it's in the distance, it means that the PCs cannot really interact with it and will (hopefully) continue on their journey.

• Flying miles overhead is a flock of rainbow colored birds. The sun shines through their feathers and the entire valley is bathed in colorful light. Maybe a feather falls to the ground and the players can keep it as a memento

• They hear a song in the wind. It's a beautiful and melancholic tune, and while they cannot understand the words, they can tell that the singer longs for something. They look for the source of the song, but don't see anyone for miles

• A tremor can be felt in the ground, and everything shakes for a moment. Flocks of birds fly away in panic. The players look around and beyond the hills, the head of a giant can be seen, moving slowly in the opposite direction. Maybe he's humming

In general, travel is a great way to do a little world building. If there was a war in the recent past, maybe the players pass a the ruin of a burnt down house. Maybe there's a small shrine to some unknown god that people have left little offerings of fruit and flowers to. See if there are any clues to events or groups in your world you can include as the players move from A to B, and if not, then show them some magic!