The still of the night
Definition 1 of 1
Pro Tip 1/3Literary Atmosphere
Often used in literature to set a scene of silence and darkness. 
The novel opened with the hero pondering life in the still of the night.
Pro Tip 2/3Emotive Usage
Implies a personal or emotional moment of reflection or solitude. 
She whispered her secrets into the still of the night.
Pro Tip 3/3Not Literal
Does not always mean a literal time at night; may refer to any very quiet moment. 
In the still of the night, even the busy city seemed to sleep.