in the middle of a field; in the fields
Refers to being physically located within a field or open area, often implying a rural or natural setting.
An old house stood in the middle of a field.
He got lost in the fields.
Compound of 野 (no, 'field') and 中 (naka, 'inside'). The reading のなか is a straightforward combination of the kun'yomi readings of the two kanji.