Thanks for the reply! Those sound like great ideas. A shame it didn't work. I can't mod at all so I've no idea how complex things are. Still, this mod is a vast improvement for underground play so I'm grateful at least this was possible.

To be honest, i wanted to make passages in mountains, some unclaimable underground water-lake provinces claimable but unlike with "tunnels", it has no separate labels related it forcing me to make much more complex workarounds, modding this game is really sketchy and stuff related to world generation are really complex by its nature. Im afraid it beyond my skills and patience to do that, i admit that im really not experienced modder enough to create this stuff so unless game developer simplify structure of assets, i wont make mod affecting it.

This makes such a huge difference for underground play. I've had similar mods before but they've all stopped working, so I'm grateful to see someone "fixing" this again.
Is it possible to inculde underground river provinces too? I noticed those are still unclaimable.

This Mod 10/10

Mod is also compatible with Ogre 1.0 Update (released 01.04.25) so there is no need to update this atm.