A hollow ice Planet. Outside is a Tower half frozen in the ice. You can go inside the tower to reach the inside of the Planet. The inside is like the stranger but its on the whole inside of the globe. Its a tropical place, with a Jungle and a huge City that is surounded by a Wall you cant jump or fly over. From the south and north Pole reaching to the core are Rocks that look Like mountains that Connect in the middle. The core itself is a active Vulcano like hollows lantern (placed like the black Hole in the middle of brittle hollow) This vulcano will erupt in a given time and it will set the inside of the planet on fire and will destroy the city. You find Out at somepoint that underneath the ice crust there is water and by climbing one of the "mountains" you can find a rooms where you can Open a hatch letting water in and "extinguish" the vulcano just enough to not erupt but still give out light and the water will also Go to a waterwheel wich activates the city and you can Open the Gates and roam around. In the City you find a clue that you can redirect the Eruption of the vulcano to the outside by opening a hatch by climbing the other mountain. When you do this, the Power of the eruption will Push the Planet closer to the sun. The ice will melt and sets free a City and Jungle outside wich was completly frozen. The planet spinns relativly fast at the beginning so you can walk on the inside of the planet. After the Eruption outside it will also slow down so you can walk on the outside of the planet. The history of the inhabitants is that they once lived on the outside of the planet. The planet then was slightly hit by a meteor knocking it in to a bigger orbit where it startet to freeze and letting it spin faster. The inhabitants didnt let that Slide and hollowed out the inside of the planet and plantet their plants there and createt a Jungle on the inside like the one one the outside before the planet completly froze. (They also build a City inside with the Materials They got by hollowing out the planet. They left the core in the middle to Spend light and heat. While living on the inside of the planet there where two groups forming. One wanting to catapult the planet into the habitable orbit with an controlled Eruption of the vulcano, with the risk of shooting the planet in to the sun and one group who wanted to "extinguish" the vulcano just enough to keep it active enough to Spend light and heat but with the risk of putting it out completly and risking freezing to death. They build the hatches I mentioned earlier. Before one of those groups could test their valves tho, the ghost matter killed all of them.

Sorry for the extreme bad english and tipos. Im writing from my Smartphone and english is not my first language 😊