One of my favorite experiences, when I worked for the Boy Scouts of America, was that of walking through the woods, alone, listing to the birds' calls, the leaves moving in the wind, and the crunch of the under story beneath my feet. There is something uniquely spiritual about this. It felt like you had the unique privilege of coming close to seeing god's wake.
Habitat was a similar experience. While we didn't build a house, we contributed to a project that will allow the local Habitat affiliate in Vineland to build more than a single house each year. They plan on doing two houses a year but I can see them coming into the position to do three or even four a year. This trip brought back memories of fixing houses with Appalachian Service Project back in high school. Service to others, like nature, is a uniquely spiritual activity.
I consider myself an Agnostic Theist. I accept the fact that people who try to prove the existence of god though science or philosophy are trying to do the impossible. We have to make a Kierkegaard's Leap of Faith. In the face of this, I still believe. I can't help it. I have tried not to but have failed. Something within me overrides my logic and still has hope that there is something more than this life beyond the void. These sort of experiences are the reason that I have belief in a God.