Squirrel, I'm willing to add a few more underground lakes to the map. The good thing for the Usurpers, about the underground lake idea is that not only do they exist in real life but there's nothing that says they cannot be connected to each other via a series of "underground" streams, tunnels, crevices, etc.
And this could make the Usurpers, very powerful indeed because I could link these lakes via undeground connections that don't have any logical surface counterpart. 4 or 5 more in every corner of the globe and you've got a nation which will have the exclusive ability, early on anyway, to move from one side of the map to the other, and pop up and attack anywhere. And build 20 or whatever coastal forts around these 4 or 5 lakes. The flipside is that once Agartha and the human players can get into the water and get to one of them, they could attack R'lyeh cap directly. A fix is to have only one of these connect directly to the cap, with the others connected to each other.
The problem is the map is jam packed as it is, where to put these extra lakes, so they don't obstruct the land routes between AI, magic sites and opposing teams. This map is actually bigger than the current one. Remember, magic sites are purple X's. I could make the central magic site (the most powerful one) an underwater magic site, but don't know where to put the rest. Squirrel?

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Be harmonious, enrich the soldiers, and scorn all other men.
-Emperor Septimius Severus, to his sons shortly before his death, quoted in Dio Cassius (77.15.2).