unbelievable

The athlete showed unbelievable speed during the final hundred meters.

(Chinese) 这位运动员在最后一百米展示了令人难以置信的速度。

It is unbelievable that he finished the entire marathon without training.

(Chinese) 他居然在没有训练的情况下跑完了整场马拉松，真是不可思议。