Student or Learner
It is not until we visited Hue that we know about its beauty.
It is not until we visit Hue that we know about its beauty.
(This is a general statement that applies to everyone. It means you can't appreciate Hue's beauty without visiting it. This sentence could appear in a travel book.)
It was not until we visited Hue that we knew about it's beauty.
(This is a personal statement based on your visit in the past.)
You could say to someone else:
It is not until you visit Hue that you will know about it's beauty.
(You will not know about the beauty of Hue until you visit it).