This is actually a variant of the “Play by Email” feature indirectly supported in Civilization 5. For more details on how it works please see this answer on arQUade.
As helpful as that answer is, it’s also cumbersome to just email a save back and forth between players. It gets especially messy when you have more than two players. A bunch of nice people have built Giant Multiplayer Robot as a way to solve the issue. Frankly, I think it’s a wonderful service and plan to try it out soon.
However, there might a situation when you just want to play a long Civilization game with just a single friend or family. If you both use Dropbox, the following would easy the bother of manually transferring the save file back and forth. Please backup any hotseat save files before you try this out! And have a shared dropbox folder with your play-partner.
Start up the command line in “Administrator” mode. Go to Start and do a search for the program “cmd”. Right click it and have it “Run as Administrator”. Refer the following screenshot.
From the command line, navigate to the Civilization 5 save game directory. On Windows 7 you can do it with the following command,
cd "C:\Users\AbrahamV\Documents\My Games\Sid Meier's Civilization 5\Saves"
Obviously, you need to change the username to how it is on your system.
Now you need to delete the existing hotseat savegame folder. Please backup any save games you have in there before you continue. To delete from command line, use the following command,
rmdir /s hotseat
The above will delete the ‘hotseat’ folder and any sub-folders in it. Don’t worry, we’ll re-create it.
Now we need to create a symbolic link to the shared folder in dropbox. Use the following command, but change it for your respective folder structure.
mklink /D hotseat "C:\Users\AbrahamV\Dropbox\For Bro\Civ5_saves"
You can close the command line window after this.
A symbolic link is a special kind of shortcut. What it does is create a shortcut to the desired folder, but other programs will see it as an actual sub-directory instead of a shortcut. This way, we can use Dropbox to synchronize our savegames but as far as the Civilization-5 game is concerned, things are normal.
Have fun playing with dropbox !!