Bu kitap kahramanın aşılmaz olasılıkları fethettiğini görür ve günü kurtarır. - This book sees the protagonist conquer insurmountable odds and save the day.
Bu aşılmaz gibi görünebilir. - This might seem insurmountable.
A problem that is insurmountable is so great that it cannot be dealt with successfully. The crisis doesn't seem like an insurmountable problem. = insuperable. an insurmountable difficulty or problem is too large or difficult to deal with