keep your eye out for an ememy prophet, DOW and capture it. They retain the original religion. Then use it on your cap yourself.
Tried this, it doesn't work. If you convert the holy city yourself (with a missionary or great prophet, even if those guys are a different religion), it doesn't count. The computer needs to do it in between turns so you get the red "your city has been converted" message.
Found your religion as late as you can, so that the pressure of other religions will be big enough to indocrinate you. Pangea is best for this I think. Found the religion in a city close to a civ with already strong religion. Dont spread your religion.
I've tried that as well but it didn't work very well. I had a holy city which should have naturally converted due to the insane amounts of pressure from other religions but after a long time, it just wouldn't convert so I abandoned that try.
In theory, it might work though. I actually thought a good approach might be to try an Into the Renaissance game as Austria, Diplomatically Marry the Vatican City, and then beeline Humanism so that the Protestant Reformation can sweep through Europe (and hopefully the Vatican). I actually started a game for this, but decided it would be easier doing a Duel map instead. (I also learned that Into the Renaissance with marrying the Vatican + Aesthetics and Pledging is supreme overpowered, especially since it's not uncommon for 3-5 city states to all want you to wipe out the same barbarian encampment).
Best way to get this achievement is to not try for it. Just play normally and eventually some prophet will be eyeing ur holy city and go, hmm, good place for buddhists to spread for celts.
You would think, but it just doesn't happen that often. I've been playing G&K since it came out and AI's just don't seem to like converting me!
What size maps are you playing? Seems obvious, but you're much more likely to suffer this achievement on a smallish map.
I think this was helpful.
I did (finally) get it. Previously I was trying Standard/Large maps with multiple religions, on the hope that one of the many religions would try to take me over.
Instead, I tried a Duel map (me as Boudicca and AI as Pacal) with no city states, so there was no one to convert but me. Figured that with the Mayans' "8 Religion" value, the Pyramids for faith, Pacal's natural beeline toward Theology, and being able to found/enhance a religion quickly with the Long Count, that he would be a good choice. Still took him a long while to convert me. I even intentionally left him Stonehenge, Great Mosque, and Hagia Sophia to build so he could focus on religion. Ironically enough, he converted my holy city last. I had my capital and my second city far away from him, but built my third city (which I made my holy city) right next to his capital. Still, he send his missionaries far to my first two cities before converting the neighboring holy city.
Glad I've got that achievement over with. Thanks for everyone's help and suggestions!