The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Choose the missing words of the phrase or sentence.

Summer is the ideal time for one of the great outdoor activities, hiking. It is much more than just a great workout. You breathe in the fresh, clean air while the city life you have endured all week just fades away. When hiking in the deserts, you suddenly realize that life is precious and you will think deeply about your life. 

Hiking is a(an) （） activity.