I love the idea of a far north civilization who uses the sea - as in, whole guilds of seafarers, from the seaweed harvesters (whole complex ecologies of sea plants and small shellfish, creating all the nutrition they woud need) to the whalers (or whatever large, blubbery creature could provide a host of other uses when triumphantly killed) to the hunters of slippery seal creatures that provide the skins for clothing, drums, waterskins, etc, to specialists mining the ocean floor for minerals and other goodies that serve the civilization. On land there are "ranchers" who grow millions of mouse sized furry creatures in bins, use their body heat for warming greenhouses, and then eat them in mass quantities. They disdain the poor teeth and flabby musculature of those grain eaters to the south, and regularly send maori style raiding parties to scatter the weak tribes living nearby. Generally speaking in biology, there is a tendency for animals in the northern range of the species to be larger than those in the south, so maybe these folks are huge, and flabby from mass consumption of fat. Smooth white skin, tattooed with squid ink, carrying obsidian spears and with bright blue eyes. I like the idea that underwater volcanos cough up minerals, and probably their theology is based on the gods that live deep under the sea. Volcanic rock signifies power, and heat=status, so the richest and most powerful folks flamboyantly waste heat, and are skinnier, since fat=survival here. They have priests of the light (summer solstice) and of the dark (winter solstice) and the whole culture revolves around the sun, essentially becoming more vicious and warlike as the sun fades, to essentially vampiric in the long months of whole dark, but then undergoing extensive rituals of fast and redemption throughout the spring to enjoy a few months of great wisdom and compassion in the summer. This is when their books are written and children are born, and then trusted monks hide the trappings of the "light" civilization away when the descent begins in the fall.