Dwarf Tunnels

The main reason the species held together culturally for as long as it did, the Dwarf Tunnels have always been the fallback, and the natural starting point of Dwarves.

The first ones built their tunnels through the south pole, virtual ant tunnels in that one, they're a glorious network made for travel between the major established internetworks that are more or less cities as established.
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As The Dwarves continued to burrow, they found more places to explore. They also found where not to explore. Turned out the ocean isn't always as deep as all that, and once they learned some magic, the dwarves were quite good at delving and spreading out.
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They were global before The Scribes were Established, though pockets here and there were unreachable, due to locals, wildlife, magic, or natural land issues.
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Some have collapsed in the times since they've been regarded complete, and there are several major tunnels that are used by others as means of travel. Networks spread from them and it's hard to find a place a dwarf community is far from for this reason.