How to Design a Fictional Subterranean Metro Map and Travel Guide Using Claude and Midjourney

There is a distinct, slightly eerie charm to transit maps. They take chaotic, sprawling cities and simplify them into clean, colourful lines. But what if the city in question didn't exist? And what if, instead of sprawling across the surface, it existed entirely underground—a subterranean metropolis carved deep into the Earth's crust, lit by bio-luminescent moss and geothermal vents?

Creating a speculative world is one thing; making it feel lived-in is another. A fictional travel guide, paired with a detailed metro map, is a brilliant way to ground your speculative fiction, D&D campaign, or world-building project.

By leveraging Claude for world-building and text layout, alongside Midjourney for atmospheric concept art, you can design a gorgeous, believable travel guide for a city beneath our feet.

Step 1: Mapping the Subterranean Transit Network

Before we draw anything, we need to understand the geography of our underground city. Let us call it Sub-London—a Victorian-era mining colony that expanded downward when the surface became unlivable.

Instead of standard streets, people travel via massive steam-powered pneumatic trains and funiculars. We need transit lines that reflect the social strata of the deep.

Start by asking Claude to design the transit network. We want distinct lines, each with its own cultural identity and safety rating. Use this prompt to get started:

`text Create a transit map directory for 'The Deep-Line Metro' in a Victorian-steampunk subterranean city. I need four distinct lines: 1. The Brass Line (connecting the wealthy geothermal estates) 2. The Sulphur Line (running through the industrial mining sectors) 3. The Moss Line (weaving through the bio-luminescent agricultural caverns) 4. The Abyss Line (an abandoned, high-risk line descending into uncharted territory) For each line, list 4-5 key stations, their atmospheric description, and one crucial local transit law or safety tip for travelers. `

Claude will generate a wonderfully atmospheric directory. You will get station names like Fossil-Gate, Glow-Worm Siding, and The Chasm's Edge, alongside practical, dark-humoured commuter advice like: "On the Sulphur Line, passengers are advised to wear their brass respirators between the hours of three and five bells, or risk permanent vocal damage."

Step 2: Writing the "Local Etiquette" Guide

To make your travel guide feel authentic, it needs to read like a real brochure you would pick up at an information kiosk. That means incorporating mundane details: ticketing options, local customs, and things that would baffle a surface-dweller.

Use Claude to write the introductory page of the travel guide. If you want to dive deeper into the technical mechanics of how LLMs structure these complex writing styles, check out our glossary entries on system prompts and creative constraints.

Prompt Claude with the following:

`text Write a welcoming but slightly ominous introduction for 'The Surface-Dweller’s Guide to the Deep-Line'. Include a section on local customs, such as how to properly greet a Geothermal Engineer, the etiquette of sharing oxygen masks during high-emission delays, and why you should never look directly at the train conductors. `

Claude excels at this dry, world-weary tone. You will end up with a travel guide that warns tourists against using "surface-born idioms" and explains the delicate etiquette of purchasing "compressed-air tokens" from local street vendors.

Step 3: Visualising the Underground Stations with Midjourney

Now, we need visuals to accompany our guide. We want to capture the scale of massive, cavernous train stations where copper pipes climb wet stone walls, lit by the eerie glow of green bio-luminescent algae.

Midjourney is perfect for this, but you must avoid generic "sci-fi bunker" aesthetics. You want to lean into industrial, historical, and organic textures. To see how other artists capture these complex, mood-lit architectural prompts, check out the community showcases on the Midjourney support site.

Use this prompt structure to generate a stunning visual for your travel guide:

> /imagine prompt: A cross-section architectural concept art of a Victorian steampunk subterranean train station, massive cavern carved from dark wet basalt, steam-powered copper trains on tracks, glowing green bioluminescent moss on the walls, travelers in heavy trench coats and brass goggles, cinematic lighting, moody atmosphere, Arthur Rackham style mixed with retro-futurism --ar 16:9 --v 6.0

This will give you a striking, atmospheric image of a station that looks as if it has been carved directly out of the stone, perfect for pasting into your travel zine.

Step 4: Assembling Your Guide

Once you have your text and your concept art, you can compile the entire guide. If you want to draft a rapid web-based prototype to display your guide as an interactive web page, you can experiment with Figma Weave to design a sleek, terminal-style interface where users can click on different metro stations to read Claude’s local guide text.

Before you know it, you’ve got a fully-fledged underground world that ticks all the right boxes, ready to be handed to your players, readers, or fellow world-builders. It is an incredibly rewarding way to turn simple text prompts into a tangible, immersive piece of speculative design.