This illustration depicts a fictional city design, established on the recently discovered exoplanet TRAPPIST-1d by the crew of a failed mission and its descendents. It shows a cross-section of the cave system in which the main city is located, along with details of the city and native plant life along the borders. At the top is the historical district, which preserves what remains of the original settlement established by the crew of the mission. The libraries, museums, and public service buildings are located here. At the lower left is the botanical district, established later when the inhabitants established building methods that could withstand the high winds of the exposed area within the arch. This is where Earth plants are grown from seeds brought with the original crew, inside of large indoor facilities where the climate and lighting conditions can be reliably controlled. The city proper is built inside of a man-made cavern in the center. This is where the majority of the citizens live, as well as the location of most leisure activities. To the far right, a secret settlement exists within a largely otherwise unexplored cave system. This settlement was created by citizens who became dissatisfied with their place in the city's societal structure. The cave is also populated by bioluminescent creatures, whose properties then are transferred to those who live around them and ingest them. Because of this luminous quality, those who live in this cave are treated as a sort of urban legend by those in the city proper; their presence in the public mind is somewhat like that of ghosts or other supernatural beings.
Detail 1: A group of friends watching a wind race. Because the wind is so powerful, the inhabitants of the city use it as their primary method of transportation, but it is too powerful for flying safely. Instead, they use gliders attached to sails controlled by electric motors. These gliders are also used for sport, though racing them is highly dangerous.
Detail 2: A farmer checks on a crop of native plants. Farmers are highly respected in this society because the conditions outside of the city are so hazardous, and therefore only the strong and technically skilled are able to handle the job. Health is highly valued by the society, and therefore jobs that require physical strength or skill are highly valued.
Detail 3: A memorial statue dedicated to those who lost their lives during the failure of the original mission. It faces towards the side of the planet that eternally faces the stars.
Detail 4: A cross-section diagram of the mountain in which the city is built, showing the path of the springs that feed it. The mountain prevents the rain clouds from crossing the terminator, thus keeping the city in a rain shadow.
Detail 5: A view showing the play of light on the roof of the cavern that houses the city. Because of the low light, citizens make sure that what light they have goes as far as it can.
Detail 6: A gondola driver transporting a passenger through the canals that criss-cross the city.
Detail 7: A view into the mouth of the natural cave opposite the city. Citizens of the city do not enter this cave for fear of what monsters may live there. Only the highest levels of the government are aware of what actually lives there.
Detail 8: The settlement within the bioluminescent cave. Many of the people who live here are those with genetic defects or other physical disabilities. These people are not treated well by the larger society, which treats physical health as a measure of a person's value to society. Others are simply unsatisfied with the seemingly arbitrary rules imposed upon them by a society that is obsessed with the preservation of Earth traditions. Those who live here often travel by zipline, which is practical due to the water-logged nature of the area and the height of the dwellings they've carved from the massive stalagmites in the cave. It is also helpful for those with limited mobility. Otherwise, they travel in thin, canoe-like boats.