The long and short of Celtic Christianity is that it celebrates the beauty of nature--humans, animals, waterfalls, trees, all of it--as God's love letter, and that there are sacred places in nature just as churches are held to be sacred.
There are some very beautiful writings; I highly recommend John O'Donohue's Anam Cara or To Bless the Space Between Us. To learn more about Celtic Christianity, check out Celtic Spirituality, and James Mackey's Introduction to Celtic Christianity. Study St. Clare, St. Francis, and St. Brendan, St. Columba, and Hildegard of Bingen. And, you know, go outside.

And ask me if you have any questions. I'm still learning, myself, but I'll go looking for answers if needed.