If it's in Hanoi or Saigon, I didn't see it.

We also went to Halong Bay and the Mekong Delta. Didn't see it at either place.
BTW, I like the picture. If I had seen that tomb, I would probably have taken a picture of it. On seond thought, we did go to a place in Hanoi that had some old buildings that looked somewhat similar to your picture. I'll try to dig it up and post it.