Eating outdoors feels great.
The outside temperature was below freezing.
I often spend my holidays outdoors.
Since the weather's nice, let's go outside.
It's good to get some fresh outdoor air once in a while.
野外 suggests open fields or nature, often used for outdoor events like 野外コンサート, whereas 戸外 simply means the space outside a building.
外 is the common, casual word for 'outside', while 戸外 is more formal and typically appears in writing.
Compound of 戸 (と, 'door') and 外 (がい, 'outside'), literally 'outside the door'.