Translation:Let's take the train there.
I agree that the suggested answer sounds better but I would not be impossible to say: let us go there by train
Agreed, "Let's go there by train" is a fine translation, too.
I have added it 10 months ago, just forgot to comment.
"let us go there by train" is still not accepted
It is among the accepted forms. Next time you should report using "My answer should have been accepted".