Poseidon is the 5th moon of a gas giant, about 3 times the diameter of the earth but far less dense so sports 0.8 Gs. a water world in the extreme. with an average oceanic depth of 100 miles and the massive gravitational effects of it's primary and sibling moons, Poseidon is extremely volcanic and stormy. it's daily tides and waves are hundreds of feet high with hurricane force winds and near constant mildly acidic rains. the planets only life consists of a soup of microbes that keep the moon's atmosphere oxygenated to 40%.
so, whats the motivation to colonize this highly inhospitable world? the ocean is a toxic cornucopia of exotic minerals and chemical elements and isotopes. lower a pipe down deep enough and you directly tap most of the elemental periodic table.