Once you have Templar forts in your game, make a save, as this will involve a bit of trial and error. Blood Rage and Therianthropy are required for this achievement. Recommended abilities are Travel Speed 1, Dark Ritual 1, Adrenal Surge, and Dark Infiltration.
With this setup, you want to travel to the nearest Templar fort and go into a blood rage. When the fort is destroyed, continue the process onto the next one. Ignore the popup that your vampire is close to death and keep going until your vampire dies.
Reload your save and follow your previous path, making a save before traveling to the final country. Use blood rage again and heal up somewhat. To end prematurely, travel to the next country when your health is high enough. On casual difficulty, the health bar was just below the horizontal section of the cross when I did this successfully.
The fort needs to be destroyed after the popup being close to death. If the fort is destroyed at the same time, it won't count. However, if the vampire and fort die together, the achievement will unlock.