I'm especially curious in the case of fantasy settings. I'm admittedly not super well read in the genre, I know about the Ways from the Wheel of Time series[^1] , and I'm sure D&D has its fair share of fast travel mechanics.
Anyway, in my case I use mass routers. Rather than a dry lore dump here's a slightly less dry lore dump in story form!
spoiler
He glanced nadirward through the observation window at the green and blue surface of the planet. A river, coruscating in Focus's rays, wound through the verdant jungle passing below. It was THE river, the measure to which all other rivers were compared. It was so old that it didn't even have a name. Every other river on Yih, and every watercourse wrought on other celestial bodies by pioneers in the intervening millennia, was, after peeling away one hundred thousand years of sound changes and semantic drift, named after this river.
But he had seen this sight countless times, and it failed to put his mind at ease. He spun the metal prayer ring on his writing claw, feeling each of the twelve teeth pass under the pad of his outer thumb. The ring had belonged to one of his sires, who had often handed the shiny trinket to him to amuse himself with when he was barely a pup. It had been years since he had prayed it, not until this morning just before being shriven. It had been years since he was last shriven, too. He'd be the first to say he wasn't the most pious Wayfarer, but there was a real possibility, however infinitesimal, that today his life would come to a messy end, and he wanted to have a clean conscience if it came to that.
He turned to face the cause of his anxiety. Attached to a bulkhead opposite the window was a cylindrical machine barely larger than a suspension capsule, with a bore just large enough to fit a single yinrih, and maybe a satchel if the yinrih in question was particularly svelte. He floated over and looked through the bore. It was like he was staring down the business end of a railgun.
«You're going to be fine, Hearthfire.» He tried to reassure himself. «Nothing's going to happen. We did gross upon gross of tests. Equator to pole, Low orbit to surface, surface to moon, even interplanetary hops, all the way from Hearthside to Moonlitter. Inert object tests, live tests, and all the tree-dwellers we sent came out perfect.»
«Except Moonbeam.» nagged a tiny voice in the back of his brain.
«Poor Moonbeam. I know you're not supposed to name them. Makes it harder when... That happens.» The little tree-dweller went in fine, but the impulse buffer on the egress router failed as she dropped back into realspace on the surface, retaining all the momentum from the ingress router in orbit. In the span of a temporal quantum she ceased to be biology and turned into physics, ending up impacting the opposite wall at 20 times the speed of sound. The barrier was built to take it, but her poor body wasn't. She ended up a maroon smear on the wall.
«Time to get strapped in.» said a sandy-furred engineer floating next to the mass router.
He took a deep breath and floated into the bore, slipping his forelegs into the harness, then his hind legs, then his tail, and finally his head.
A voice came through the earpiece around his left ear. «Hearthfire, this is Morningstar. Everything's up and up down here.» It was the same cleric that had given him absolution this morning. «Just for review, you're being routed through an intermediate router on the surface before egressing at the antipodes. The impulse buffer is good on both the intermediate and the egress, in case a packet gets dropped along the way.»
«Ingress and egress buffers are synced.» Said the sandy-furred engineer.
«Acolyte, begin the countdown. May The Light illuminate your way, Hearthfire.» Said Morningstar.
«Twelve...» The sandy-furred engineer began solemnly sounding off the numbers.
«Eleven...» In a matter of seconds, a thin sheath of realspace containing Hearthfire's body would be shunted into the Underlay.
«Ten...» This realspace bubble would be encapsulated into billions of discrete packets.
«Nine...» From the perspective of a hypothetical observer embedded in the Underlay, these packets would appear discontiguous, and could take separate paths to reach the same destination.
«Eight...» But from the perspective of an observer contained within one of these packets, the entire space would still be contiguous.
«Seven...» Blood would still flow, and nerve impulses would still travel uninterrupted.
«Six...» Or they would if the traversal through the Underlay weren't instantaneous.
«Five...» Hearthfire's stream of consciousness would not be broken.
«Four...» There would be no ontological question that what emerged from the egress router was the same Hearthfire that entered the ingress router.
«Three...» These packets would hop instantaneously through an intermediate router directly below at the surface.
«Two...» This router would, in mere nanoseconds, direct the flow of packets to an egress router at the antipodes.
«One...» The egress router would absorb all the momentum that Hearthfire had while in orbit before shunting him back into realspace. Should the intermediate router drop a single packet, the whole flow containing Hearthfire's mass would be shunted harmlessly back into realspace at that router, provided it, too, absorbed his momentum correctly.
«Zero.» Hearthfire felt a tingling sensation, as though his whole body had fallen asleep. The feeling lasted but a fraction of a second, then he felt the weight of his body pulling him down. He had made it. In less than the blink of an eye, he had gone from a space station in low orbit over Yih to a lab on the surface on the opposite side of the planet. Hearthfire was the first yinrih to traverse a mass router network, and he had done it without a hitch.
This was going to change everything.
[^1]: fun fact: the Ways inspired the Nether from Minecraft insofar as one step in one dimension is multiplied in the overworld
I like a SciFi setting where Portals are the primary means of FTL transit, essentially destructive replicators that disassemble the entrant at one portal, transmits their quantum structure via entangled particle communication, and reassembles them on the other side. The consequences of this are that matter/energy balance must be carefully managed on both sides with stockpiles of raw material to replicate with and the energy to drive it being essential.
Now this method has an obvious flaw, as it doesn't account for traveling to new sectors of space. As such, an alternative method was developed for exploration. This amounts to a mass driver driven by a singularity. An autonomous vehicle amounting to a hardened Portal with interplanetary grade thrusters and a special counter-balance is built and deployed in a system close enough to a singularity to allow transit to it within a few months time.
A vector is calculated with quantum precision. A follow vehicle launches with the FT module held with in it. As the vehicles approach the singularity and gravity acceleration takes hold the follow vehicle fires a high intensity beam array serving to both revers it's own thrust, accelerate the FT module, and provide a protective channel for the module to approach within. High velocity particles are a major threat approaching a singularity, they must be deflected.
The FT module accelerates as it approaches the singularity, beginning orbit, as it orbits the counterweight section is thrust down away from it closer to the singularity, akin to a space elevator, using the same beam tech as the follow vehicle. The counterweight accelerates faster than the FT Module, while cintrepetal force creates a slight outward vector. The vehicle approaches relativistic speeds. Once in the target velocity range, generally 80% of light or .8LS, an antimatter annihilation charge is set off at the base of the FT Module severing the counterweight and propelling the FT module out of orbit and onto its final trajectory. The mother of all slingshot maneuvers.
If the FT Module is release from the gravity well successfully, is on-vector, and has survived functional, the portal onboard is activated, converting mass from the vehicle into subatomic particles to feed the beam and further thrust the vehicle until the thrust-midpoint of transit, by which point the vehicle may have approached 90%+ LS depending on the distance of transit. At this point the the beam is inverted, firing in the other direction to decelerate the FT Vehicle. Typically the target will be another highly massive body, such as another singularity or neutron star, which will be used to decelerate and re-vector towards a local system where another antimatter annihilation charge is used to overcome escape velocity and achieve orbit.
The FL Vehicle may then be commanded via entangled communicator to use its Portal to construct harvester drones to harvest mass from local space until enough mass is gathered to replicate an expeditionary vessel.
Given that none of this process is FTL, it takes many many years between launch and arrival of a portal in a new system. So the question is, who is in command when it finally arrives? What has culture, politics, and biology done in the meantime?
It is a good setup for either side of the portal, on the one hand you have PCs as expeditionary forces heading into an unknown system after many years of process to get there. On the other side you have a Stargate type scenario where a portal ship is discovered in local space. Where could it lead?
In both cases there is the opportunity for a fun bit of Deus Ex Machina, as you must decide just how autonomous the portal ship itself is. Are they dealing with a sentient ship that has been on a solitary transit for years of its own relative time, but centuries of outside time? An anachronism of the old order. Is the portal an inscrutable presence with only the need to feed itself mass and perform its function... and your team doesn't have the codes or features of it's masters? Or even, is this just a fancy automatic door which activates as soon as any being approaches close enough to be sucked in and spit out at wherever it was last programmed to route to? Leaving the PCs in suspense on this point is a lot of fun.
#FTL #TTRPG #SciFi #GM #SWN #StarsWithoutNumber #Starfinder #Traveler