This is a great blog post from a teacher re-learning the value of creative free play and specifically outside.
I highly recommend you read the whole post, but for me this sentence summed up the whole experience:
“…As I witnessed these projects I realised that children and adults can only be as creative as their environment allows them to be and that by letting children spend time in a natural environment like the woods or to be surrounded by loose parts, we can but only help them to become or remain creative.”
Read the entire post: Learning for Life: Loose Parts = Creativity. Road Trip to Lithuania Part 3.