... strange forests that, because of the inclination of the Earth’s axis, grew in almost permanent darkness at the south pole. “These forests of the polar night,” Nield explains, describing an ancient landscape in the present tense, “withstand two seasons: one of feeble light and one of unremitting dark. Today’s world has no equivalent of this eerie ecosystem. Their growth rings show that each summer these trees grow frenetically. Those nearer the coast are lashed by megamonsoon rains roaring in from [the lost continent] of Tethys, the thick cloud further weakening the feeble sunshine raking the latitudes at the bottom of the world.”
- this from here on the subject of 'no-analogue landscapes', environments that have existed once and never again. The polar forests of the Cretaceous were the products of an extreme greenhouse effect and overflowing seas, providing for thick vegetation even at the poles
Obviously, this is an outrageously good environment for adventuring. Endless night, endless light problems, endless frost, vast beasts angry at the disturbance. Definitely the north of Vyrhrad has polar forests like this. There are dinosaurs and colour-appropriate dragons (white, green, black) and...chiefly dinosaurs, I guess? The Monster Manual wants me to have remorhazes but I don't really like remorhazes. The bigger dinosaurs will pick their teeth with them They are the dry(ish) land equivalent of the northnorth. Players are destined for them.
But more than this specific environment, point is: there are and were and will be amny more environments than exist right now. All such fucked-up places that your mind conceives are possible. Probably they have already happened. Make them happen.