The Dry Season
The underlying networks of tunnels, caverns and even rivers and lakes beneath the islands are collectively referred to as The Catacombs, and they are generally dismissed as quite literally beneath the notice of the ‘real’ nations of the islands. A forced and often violent mix of humans, elves and orcs makes up most of the population. Few gnomes are ever exiled from their own communities or discontent enough to leave, and so the gnomes found beneath the islands are usually the strangest of a strange species, under-sorcerors with powers over rock and wind or leaders trying to bring life and prosperity to the battered communities around them.
Each of the islands has ‘official’ entry points to the catacombs – while smaller landings might be used by smugglers or pirates, every island has at least one fortified entrance that marks the primary gateway to the underisland. Thick, roughly-formed walls and towers mark these gates. They are formed out of anything available – often the rock hewn out of the underside to make room for the first exile communities is repurposed for them. These gates are extremely sturdy, but more to the point, they are solid enough that any spell or explosive used to damage them will be strong enough to risk damage to the structure of the island itself, something none of the overisland communities will risk.
Beyond this, the catacombs have little in common besides poverty and danger. Their population is always mixed – no species has claimed an entire underisland for its own – but usually dominantly the same as the species living above. Orcs fleeing famine, conscription or dynastic overthrow, elven officials on the wrong side of a political squabble, and humans fleeing slavery or indentured servitude are the most common, but the different species have never been able to unite around their shared exile. Humans, used to being treated as inferiors everywhere they go, are likeliest to adapt and thrive in the catacombs, but even here they cannot escape the fact that orcs and elves will set aside their differences to keep humans in their place.