It depends on what field you interest in such landscape, architecture, tradition. In addition, It depends on your capacity to afford.
If you interest in exploring scenery, you should visit Vietnam, China or Australia, est.
If you interest in architecture, you should go to France, Russia, England, Italy, so on.
As Vietnamese, I'm so proud to welcome you to Vietnam which is a very beautiful country. You will be so delighted at its beauty, its friendly people, its tradition, its cuisine, so on.
First, Vietnam is a worthy -go sightseeing- country with blue beaches, beautiful mountains, rivers. If you want to enjoy the beauty of beach, you should go to Halong bay to enjoy the pure air, which is an UNESCO world heritage, has a thousand of islands. You should also visit other nice beaches such Nhatrang, Danang, especially Phuquoc island. Phuquoc island is like a paradise on earth, a great place to chill out with crystal clear water, long beaches. If you want to explore the beauty of mountains, you should visit the North of Vietnam such Sapa, Hagiang where you can get to unspoiled areas. It is so interesting that you visit the traditional ethnic peoples who inhabit this mountainous region and enjoy their local market. If you want to find out the tradition, you can go to Hanoi- its chaotic capital or Hue- its ancient capital or Hoian with old quarter, temples, churches, so on.
Second, Vietnamese are so friendly and trustworthy. You will very excited by their hospitality.
Third, the cuisine is so good. Vietnam food is one of the richest in the world. From traditional Vietnamese food to seafood, you will always find something worth trying. You will be so attracted by the fresh fruit you pick from trees by yourself in the large garden in the south.
Forth, the cost is so low. Especially accommodation and food are particularly cheap.
I'm self-confident to say that Vietnam is a wonderful destination you should visit once in your life.
There are many more exciting things, as its slogan "Vietnam-the hidden charm". Arriving in and experiencing.