outing to the fields and mountains
Refers to a leisurely excursion into the countryside, enjoying nature. Somewhat literary or old-fashioned; in modern casual speech, ピクニック or ハイキング are more common.
On a spring day, the family went on an outing to the fields and mountains.
Compound of 野 (field), 遊 (play/enjoy), and 山 (mountain). The exact historical derivation is uncertain, but the word evokes a traditional image of enjoying nature in the countryside.