This sentence means:

Today’s calendar hides some kind of secret or mystery.

"Today" refers to today, "calendar" refers to the calendar, and "mystery" can refer to something secret or incomprehensible. Therefore, this sentence can be understood to mean that there is something mysterious hidden behind today's calendar, which may require you to explore, discover and understand.

In traditional culture, the calendar is often considered an important divination tool that can predict good and bad fortunes in the future. Therefore, in some cases, the mystery of today's wall calendar can also be interpreted as today's calendar may imply some good or bad omen, which requires attention and attention.

It should be noted that this is only a possible explanation, and the specific meaning needs to be understood according to the specific context and background.