expression
deep down; in the back of one's mind; somewhere in one's heart
Used when a feeling, thought, or awareness exists at a subconscious or unexpressed level. Often implies that the person may not fully acknowledge it outwardly.
心のどこかで、彼の言葉が正しいと感じていた。
Deep down, I felt that his words were right.
彼女は心のどこかで、もう一度会いたいと思っている。
Somewhere in her heart, she wants to see him again.