Dear Linhthuy,
I am not exactly sure what you want. Do not forget the question marks! You will lose marks if you do not write them!
1) WHAT DO YOU VISIT? ("When you go on your walk, what do you visit?") OK.
2) WHAT PLACES DO YOU VISIT? ("When you go on your walk, what places do you visit?") OK.
3) WHAT PLACES WILL THE TOURISTS VISIT? ("When you go on your walk, what places will the tourists visit?") Good!
4) WHAT WILL THE TOUR FOR TOURISTS VISIT? NO! This is ungrammatical! What will the Tour-Bus visit, Yes! Tour, No!
Question 1 and Question 2. The questions are about something that you did in the past, several times. You have already been on several tours, in the past. "What do you visit?" means --- "What do you normally visit?"
However, Question 3 asks about a tour which is in the future!
With the information that you have supplied, my opinion is that Question 3 is your best question.
Vivilui makes many, very good points.
I hope that this helps you.
Les