I want the party to know about the stronghold and the faction. It's more that I'd prefer a slow reveal in a perfect world and I was thinking that maybe the amnesia sequence might be one way to trickle the information in slowly and alert them to possible danger. The faction doesn't want the party to know about the faction.If you don't want the players to actually even know about the stronghold yet... there's any number of "magical effects" that could keep the hold a secret. You can just make up whatever you wanted for that. Or even if you don't want to "hide" the stronghold... there's no reason why there couldn't just merely be a guard or two out front that is all friendly-like and just redirects the party elsewhere, giving no indication what kind of a stronghold it is. Heck... just put an Arcane Lock on the front door with some sign indicating it's some warehouse or something and the players might just walk right on by.
Perhaps, instead of amnesia, have the stronghold protected by some kind of ultra-subtle, but powerful, mind-affecting magic akin to Douglas Adams' "Somebody Else's Problem Field"?I'm concerned that the PCs will not accept a mere shooing, due to the nature of what they're looking for. And while I can certainly telegraph the faction's strength, the party has more than sufficient power relative to the faction to get themselves into actual trouble. Prolly still ways to handle it.
Well...the faction is sneaky and cunning and technologically advanced (albeit to no more than base steampunk levels) but unfortunately not super strong in magic. They are entirely capable of constructing something that -looks- innocuous or unpleasant; or maybe drugging someone so they're addle-headed and don't perceive things normally. But auras that induce mass delusions are probably beyond them.Perhaps, instead of amnesia, have the stronghold protected by some kind of ultra-subtle, but powerful, mind-affecting magic akin to Douglas Adams' "Somebody Else's Problem Field"?
Well, if it's not something they can do, maybe the reason they stick to this specific hideout and such is because they're exploiting something left behind by some other group? That could explain why nobody seems to know that there's a heavily-occupied fortress there. It would also explain part of why the denizens are so zealous about keeping people away; they don't actually know how to manipulate or control their magical protection, they just know that it works and know how to bring people in on the secret. If even one outsider were to get the secret and then escape, it could ruin their whole protection strategy and force them to waste a ton of resources on much more brute-force means of protection. It's sort of like how someone who gains immortality can actually become even more obsessed with preserving it than they were with acquiring it in the first place; once you have a fragile power, you want to ensure it will never be taken from you.Well...the faction is sneaky and cunning and technologically advanced (albeit to no more than base steampunk levels) but unfortunately not super strong in magic. They are entirely capable of constructing something that -looks- innocuous or unpleasant; or maybe drugging someone so they're addle-headed and don't perceive things normally. But auras that induce mass delusions are probably beyond them.
To build on this, 5e has a number of spells on which you could base the effect: antipathy, hallucinatory terrain, mirage arcane, etc.Well, if it's not something they can do, maybe the reason they stick to this specific hideout and such is because they're exploiting something left behind by some other group?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.