mystery

The origin of these ancient ruins remains a deep mystery to archaeologists.

(Chinese) 这些古代遗址的起源对考古学家来说仍然是一个深刻的谜。

I love reading a good murder mystery before I go to sleep.

(Chinese) 我喜欢在睡觉前读一本精彩的谋杀悬疑小说。