I remember with crystal clarity only a few moments in my life - almost all were outdoors - waking up in a hammock just as dawn cracked, floating in Windermere as dusk set in, amazing memories. My children's births I also remember but the amazement and awe is overlaid with stress and worry - so yes, get outside if you want your heart to relax.
I am not a religious person but I think these are known as "Peak Experiences". [0]
I also experience "ASMR" [1] and maybe these things are related.
[0] http://en.wikipedia.org/wiki/Peak_experience
[1] http://en.wikipedia.org/wiki/Autonomous_sensory_meridian_res...