Inverted Aquarium
Arista sat quietly for a long while after the rest of the crew had drifted back toward their own stations, still watching the mermaid statue through the viewport, the same restless, familiar itch settling in beneath her ribs.
"...Everybody should be able to see this," she said finally, mostly to herself.
Bram, catching the specific, dangerous tone in her voice from across the compartment, didn't even look up. "No."
"You don't even know what I'm about to suggest."
"I know the tone. I know what the tone means. The answer is no."
"Hear me out. Hear me out." Arista turned, already half-grinning despite herself. "What if we built a dome around it? Pumped the water out? People could actually walk through these ruins, see the statue properly, without needing a submarine or diving gear or any of it."
Bram finally looked over, unimpressed. "The ruins span at least eight hundred meters in diameter, based on what we've charted so far. The statue alone's twenty meters tall. You want to build a dry, air-filled dome over an entire submerged city, a hundred and fifty meters underwater."
"...So we build a big dome," Arista said, entirely unbothered by the scale of the objection. "A thousand meters wide. Thirty meters tall, clearing the statue with room to spare."
Claire, drawn over by the conversation, studied the growing sketch with immediate, professional interest rather than outright dismissal. "...Like an inverted aquarium."
Arista brightened immediately at the framing. "Exactly that. Normal aquariums keep water in, glass keeping air on the outside. This is the opposite: a sealed dome keeping the water out, air pumped in, so people can walk around inside it while the actual ocean presses against the exterior the whole time."
"The engineering's not trivial," Claire said slowly, already working through the practical challenges out loud. "You're not just building a hull anymore. You're building a structure that has to hold back the weight and pressure of an entire ocean, continuously, indefinitely, at a hundred and fifty meters, over a footprint considerably larger than anything you've built before."
"I know." Arista was already sketching, the shape of the problem settling into the same familiar, restless excitement that had once carried her through a continental railway. "But it's the same fundamental principle as everything else I've built. Pressure differential, properly managed. The submarine hull already proves the concept works at smaller scale. This is just—"
"Considerably bigger," Bram finished, flatly.
"Considerably bigger," Arista agreed, grinning. "But not fundamentally different. Same physics. Same material questions. Just... a lot more of it."
Colm, still hovering near his charts, looked up with quiet, genuine excitement. "...People could actually see this properly. Not through a viewport. Not through secondhand descriptions. The actual ruins, the actual statue, walked through in person."
"That's the idea," Arista said, already feeling the old, familiar pull of an entirely new impossible project settling into place. "Nobody built this to be found quickly. Nobody built it to be walked past in a submarine and forgotten. If it's this beautiful, this quiet, this genuinely ancient-feeling, I don't want it to just be something five people glimpsed once and moved on from. I want it to actually be seen."
Bram studied her for a long moment, the earlier reflexive "no" clearly losing ground against the specific, familiar conviction in her voice.
"...You're not asking permission anymore, are you," he said finally. "You've already decided."
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"I've decided I want to try," Arista corrected, grinning. "Whether it actually works is a separate question. But yeah. I want to build a dome over a drowned mermaid city so people can walk through history instead of just reading about it on a wiki somewhere."
Claire sighed, though there was no real reluctance in it, already reaching for her own notes. "...I'll start on the pressure calculations. Thousand-meter span is going to need some genuinely serious structural thinking."
"I'll help," Colm offered immediately, already flipping to a fresh page in his own notebook. "If we're doing this, I want an accurate survey of the entire footprint first. Every column, every structure, mapped properly before anyone starts building around it."
Bram let out a long, resigned sigh, the exact same sigh he'd given a hundred times before across two years of exactly this kind of moment.
"...Fine," he said finally. "But if this drowns us all, I want it noted that I said no first."
"Noted," Arista said, already grinning, notebook filling fast with the rough, sprawling shape of the single most ambitious thing she'd ever proposed building.
Nettle, who had been quietly listening to the growing dome plan from her usual spot near the control station, spoke up out of nowhere, entirely unprompted.
"Hexagons are nature's strongest geometric shape. Or so I saw once in a documentary."
Everyone turned to look at her.
Bram blinked. "...You watch documentaries?"
"I contain multitudes," Nettle said, entirely unbothered, echoing the exact phrase Bram himself had used months earlier. "Honeycombs, certain crystal structures, some kind of basalt rock formation somewhere, hexagons keep showing up whenever nature needs to cover a large area efficiently, using the least material for the most structural strength. If you're covering something the size of an entire drowned city, that's probably the shape you want tiling the dome."
Arista sat with that for a moment, genuinely struck by the practicality of it. "...That actually tracks. Hexagonal tiling distributes load more evenly than squares or triangles across a curved surface, and it's efficient with material besides. I hadn't gotten that far in the design yet, I was still stuck on 'how does the whole structure hold pressure' before I got to 'what shape should the actual panels be.'"
Claire, who had been quietly sketching alongside the conversation, looked up with sudden, sharpening focus. "...If we're using hexagonal panels, I've got an idea for the joints. Instead of fighting the water pressure at every seam, we could design the connections to actually use it."
"Explain," Arista said, already leaning in.
"Spline connections, wedge-shaped edges, angled so that outward pressure from the water pushes each panel into its neighbors rather than trying to force them apart." Claire sketched quickly, showing the cross-section of two adjoining hexagonal panels, edges cut at a deliberate, interlocking angle. "The water's not fighting the structure. It's actually helping hold it together, the harder it pushes. Same fundamental logic as a keystone in an arch, the load itself reinforces the joint instead of stressing it."
Arista stared at the sketch for a long moment, delighted. "...So instead of needing every seam independently sealed and reinforced against pressure trying to pry it open, the ocean's own weight does half our sealing work for us."
"Exactly. The deeper it presses, the tighter every panel locks against its neighbors. It's not resisting the pressure differential. It's using it."
"That's genuinely elegant," Arista said, already reaching for her notebook, the whole design reorganizing itself around the new geometry. "Okay. We should head back and run this by Petrov and Gorthruk before we go any further, Petrov for the actual construction logistics at this scale, Gorthruk for material sourcing, since I have a feeling this is going to eat through metal reserves the same way the railway once did."
She did some quick, rough math on the spot, cross-referencing the ruins' estimated eight-hundred-meter footprint against a thousand-meter dome span, sketching out a rough hexagonal grid across the curved surface.
"...If we're using five-by-five-meter panels," she said slowly, working through the geometry, "covering a dome that size, we're looking at somewhere around thirty-six thousand individual panels."
Silence settled over the compartment.
"...Thirty-six thousand," Bram repeated, flat.
"Give or take," Arista confirmed, unfazed by the scale of the number, the same restless energy that had once carried her through a continental railway's worth of rail spikes already settling comfortably over her. "Good news is, we've done this before. Mass-producible components, public recipes, distributed manufacturing across however many smiths want to contribute. Same fundamental model as the metro's track sections."
"...You say that like thirty-six thousand hexagonal pressure-resistant panels is a small thing."
"It's not a small thing," Arista agreed, grinning. "It's just a thing we already know how to do, at a scale we've already proven works." She closed her notebook, already turning the sub back toward the surface, toward Petrov's careful scheduling and Gorthruk's mining expertise and an entire new project's worth of impossible, exciting scale. "Come on. Let's go tell them we're building a dome over a drowned mermaid city."