It was pitch-dark when we set out, and we quickly got lost among the winding paths.

pitch-dark 是由 pitch 和 dark 组成的复合形容词。pitch 原指"沥青"，因其颜色极黑，引申为"完全的、极度的"；dark 意思是"黑暗的"。 pitch-dark 形容"漆黑一片的、完全黑暗的"，强调黑暗程度极深。