How is it possible?
2 ways I have done it on Diety, and I have done it many times on Immortal
But like others have said "You might not even want to try...??" because when you get the setup required (Which is awesome, and rare) you probably don't want to waste it on a failed early attempt at a wonder if things don't go your way.
First of all to even have a chance, your going to have to pop a culture Ruin, and at least one population ruin. Obviously a Tech. Ruin would also help,.. Pottery great, and Writing would be the ultimate, and a milestone that might signal that there is a possibility to succeed at a Diety GL build. Social Policies required=Tradition opener, and Aristocracy.
2 ways
What I had..
1) Lake Victoria with great production sources, I think I had 3 pastures and 2 copper either within borders, or 1 tile away from my capital.
Yes, Lake Victoria. BUT I would say...Major Population Source is requirement. Maybe a early Pantheon "Sun God" with multiple wheat would work also...you get the point!
Grow as big a you can,...Then once you have Writing, "Force" production for the GL which includes Starving your city (Even if you lose population).
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What I had..
2) Settle on Grassland Masonry Hil, and bought 2 tiles to acquire second Masonry. One wheat, 2 pastures, and 1 Stone. Early Pantheon,..Monument of the Gods
Monument of the Gods?? 15% toward Ancient/Medieval Wonders...That is going to kill your game once you hit Renaissance! For Diety,...I would say YES. But it is very possible to make a run on other wonders (Snowball effect) even on Immortal which would outshine any late game pantheon.
This also requires Tech. Ruin help of Calendar or Masonry,...another would be great as well. AND, you have to acquire enough money to "Buy" Stone Works immediately.
It is the stack of 2 Masonry, Stone Works, Aristocracy, and Monument of the Gods that gives you a fighting chance for the GL.
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Picking your opponents weak in the "Wonder Building" department will also help your chances, but that normally throws warmongers into the game.
So many intangibles,...I know!
Advice,...Don't plan on trying for the GL,...BUT, if the perfect scenario falls into your lap then you might want to make a run for it,...even if it is just to say "I did it!"
I managed it a couple of times on Immortal, but I soon realised it's not worth building a strategy around it at immortal + deity.
The thing is, to reliably get it, you'd have to build the thing so fast, you wouldn't have time to research Pottery + Writing + Calendar. Why is it important to finish Calendar before GL completes? Because then you can choose "Philosophy" as your free tech, and immediately start on National College. Without Calendar you'd only be able to get free tech worth half as many beakers.
Deity is a different animal,...But playing Immortal, don't underestimate the power of the GL if you take Drama and Poetry (No Calendar)
I agree, the best strategy is Philosophy then immediately build National College, BUT...
It is not unrealistic to get 2 cities out (With Monuments) before you produce the GL.
Drama and Poetry, and Philosophy are both worth the same amount of Science (So, your not getting ripped off!).
If your going for the GL then your in probably going Tradition, and you have probably worked your way down to Legalism by this point, which means you immediately have 2 amphitheaters. And in the early game +2 culture is a big boost, which helps you close out Tradition before your opponents. Major Snowball effect,...Happiness from Monarchy (now I can build a big capital w/o limitations, Now Landed elite 10% growth and most important..Closing out Tradition (15% Growth and Aqueducts) - If your playing Casimir (Poland) it almost smarter to take Drama and Poetry because your going to close Tradition even before you could possibly build the NC.
Most Important part of acquiring the GL....??? Your opponents didn't get it, So now you have a fighting chance for "Oracle".
When I get the GL on Immortal it is not uncommon to take Drama and Poetry (Start Researching Philosophy), Build 1/2 of Parthenon, Philosophy acquired (Build Oracle), then finish second half of Parthenon. Not Common,...But I have gotten the GL, Stonehenge, Oracle, Parthenon all in the same game on Immortal with the #2 setup.