terra incognita
noun [ U ] often humorous uk/ˌter.ə ɪŋˈkɒɡ.nɪ.tə/ us/ˌter.ə ɪnˈkɑːɡ.niː.t̬ə/
未知地区；未知领域
a place, subject, or situation that you are not familiar with
Dealing with children is terra incognita to me. 对于带孩子，我一窍不通。
Compare: unknown noun