Has anyone ran a campaign or part of one in an O'Neil Cylinder?

Has anyone ran a campaign or part of one in an O'Neil Cylinder?

Yes. Jovian Chronicles.

I was actually thinking about doing this earlier today, I was thinking a campaign based on rendezvous with rama but I'm still not totally sure how to implement some ideas.

This. Seriously, everyone should play at least one campaign of Jovian Chronicles in their life.

For about 5 seconds then the PC's dropped everything to see if they could find a way to stop the spin and pop the "top" open.

I ran a campaign where the O-Neill cylinder was a generation ship that missed it's destination and has since collapsed into disrepair.

Gundam.

I like you

Not yet, but I'm actually designing a homebrew Gundam setting that will have a few of these but also McKendree Cylinders (O'Neill Cylinders with the interior size of Russia). Basically a bunch of aliens arrive after the end of a fuck-huge galactic war that saw them nearly killed off but their enemy completely wiped off. Homeworld dead, they built massive McKendree cylinders and used them as generation ships in search of a habitable system, losing most of the McKendree cylinders until they find the Sol System. With almost no power left and Sol being a good system for them to live in, they stick around.

Oh, and they are basically space elves. Why? Because I like space elves.

Wouldn't that be destroyed by micrometeors after the defense systems cease to function? A grain of sand does a lot of damage at relativistic speeds. So that limits how dysfunctional it could realistically be.

Maybe it was going to travel at just high speed, not relativistic?

O'neill cilinder vs Stanford torus. FIGHT.

Standford tori are cheaper but tend to be much smaller and as such you will feel the "pull" of the movement.

O'Neill Cylinders are much more expensive but are designed to be almost fully autonomous with it's farming areas designed to feed the colony and, if used as a mining base, could have factories in it as well to develop what else they would need for most of their repairs. And, being as big as they are, any breech that isn't catastrophic to the structure (to the point of completely destroying it, basically), the air would take days to fully vent, allowing repairs to possibly be done well in advance of full depressurization. And, thanks to just how big they would be, one would have a far harder time feeling the pull of the colony as it turns.

Stanford Tori are good, O'Neill Cylinders are far better however long-term.

I had my players visit one that was suffering from a lack of maintenance. I messed with their heads a bit:

- First thing they noticed once inside was that the sunlight was a bit green. That got them distracted for a while trying to figure out why. The reason is simple: The windows that let in sunlight were underwater and there was a bit of algae growth. After the players worked out that something was covering the windows, they wanted to know if it was dangerous, which was not a question I was expecting.

- While they were doing that, I had them making occasional awareness rolls. When one player finally succeeded, he noticed that the shadows were slowly moving back and forth. Again, a simple explanation that distracted them for a while: The cylinder was slightly out of alignment with the local star.

They then got into a fight with the locals which started a bit of a forest fire. Meaning they probably killed everyone living there.

Wouldn't Coriolis' force mess with movements?

Dropping something from one side to the other? Yeah. Playing a little game of baseball? Barely.

You can compensate with a counter-rotatory section.

That counters the spin imparted on the cylinder as a whole, but wouldn't do anything to help with what you'd feel on your section. At five miles across, they have to spin 28 times an hour for earth gravity. If you dropped your sandwich it'd fall about a centimeter out of line.

So basically most people would have no problem, though some naturally have more sensitivity to things like that. Presumably you'd select crew and all taking that into account.

Spaced habitats won't have a problem since they are likely to be big enough to not be noticeable.

They aren't 5 miles in diameter, they are 5 kilometers in diameter (3.1 miles). It would still be a fairly minor shift if you dropped something anyway.

I want to run a primitive 'fantasy' adventure in one, then have the players 'reveal the truth' and become acquainted with future tech.

I'm stuck on how to describe the environment without immediately revealing they're not on a normal planet.

Lots of fog.

Fair enough, there can be different sizes and they'd just spin at different rates. It's been a while since I read much about em and just went with what I found on wikipedia. I do like the idea of different cylinders having their own rotational signatures, so natives would know which way they're moving simply just by the effect on their inner ear.

once, but it had a HUGE radius, and was very narrow...
wait I'm thinking of a ringworld...
then no, but it could be cool...

Hologram sky. Artificial mountains filled with monsters (androids) hiding sensitive sites.

look up the comic Habitat by Simon Roy, it might give you some fun ideas.