This is the 11956th most frequent Russian word.
затылка
The back of the head.
Here, 'затылке' is in the prepositional case of 'затылок', used to indicate where the touch was felt, specifying location.
Он почувствовал лёгкое прикосновение на затылке.
He felt a light touch on the back of his head.
In this sentence, 'затылок' is in the nominative case and refers to the anatomical part that experienced the heat.
Солнце ярко светило, и его затылок ощутил жар.
The sun shone brightly, and the back of his head felt heat.
Here, 'затылок' again in nominative case depicts its spatial relative position to the source of shadows.