lost in thought

Men rowing boats on the river, reading books or newspapers, playing the piano, working at a desk or merely sitting in a comfortable chair lost in thought.

He’s lost in thought, seemingly unaware of the world around him, and he goes back to the painting.

She climbed up the stairs to the top of the tower and found him lost in thought as he looked out the window, an untouched cup of tea sitting on the table next to him.

They are all lost in thought and rarely converse with each other.

She clutches a fan in her hand and gazes pensively, lost in thought, serene, yet tinged with sadness.