Difference among 走去 vs 走路 vs 步行?
我們走去了三分鐘 and 我們走路了三分鐘 are unnatural. The common way to say it is 我們走了三分鐘.  

走去 is not a good set. We don't really use it. 

More often, 走路 is more like a gerund, and 走 alone is usually used as a verb. You can say 我們走路走了三分鐘. 

步行 could be used as a verb as it's in your example.

So, these sentences convey the same thing:


  我們走了三分鐘.
  
  我們走路走了三分鐘.
  
  我們步行了三分鐘.