Something I just thought to add too, which is kind of a random side note... The things they experienced and did, when I was making my list of ideas for them had to include a few things:
1. They had to be things that I've never HEARD of the Boys ACTUALLY doing before. I wanted the story to feel authentic in the "first time for everyone here" feeling. The only exception is the scuba diving in Chattanooga, which obviously Nick's scuba dived before. However, he was so damn excited about it, that it kind of negated the need for it to be a completely new experience for him.
2. It had to be something that invoked beauty. The point of the trip was for Brian to find something beautiful - therefore everything Nick planned had to include a breathtaking new way of viewing the world. The Grand Canyon they'd been to. The bottom of the Grand Canyon? At sunset? Not so much. The hot air balloon ride provided an ariel view without being in a "plane" persay. It afforded a closer over-head view with more detail. The Rockies with their snow caps from the lodge, the river's whitecaps, the gorge upside down (or from on the bridge)... all things that granted opportunity to see the world. Nebraska's plains allowed a view of the sphere of the earth, of great distances, of color patterns like a patchwork quilt, etc. And even the aquarium allowed an view of beautiful underwater life. It was imperative that everything they do render beautiful mental images like these... Why? Because if they hadn't seen the most beautiful things on earth, the punch at the end of Brian choosing his friendship with Nick as the most beautiful thing he'd seen wouldn't have been as powerful.