The Wandering Marquee
Feywild pocket plane, accessed via a void-sailing vessel, site
The ship's hull is scorched driftwood and stitched sailcloth, patched a hundred times over, yet it hums like a plucked string as you cross the deck. Belowdecks, past crates that smell of cinnamon and machine oil, a canvas curtain hangs in a doorway that leads nowhere a ship's hold should lead. Push through the curtain and the smell of sawdust and candied fruit rolls out to meet you, along with calliope music that has no visible source. Beyond the curtain: striped tents under a sky the color of a bruised plum, lantern-light without any lanterns, and laughter that sounds like it's been laughing for a very long time.
Nothing here bites, but the carnival's time-slip and memory-toll can quietly rob a party of days outside or of things they'll miss before they realize they're gone.
Landmarks
The Curtain of Cinder Silk. The portal itself. Anyone may push through freely; leaving requires finding it again, and it moves to a different tent each 'night.' Detect magic reveals it radiates strong conjuration.
The Hall of Losing Mirrors. A tent of forty mirrors, each showing the viewer as someone they are not. Touching a mirror lets a creature swap appearances with its reflection for 1 hour (no mechanical benefit, purely cosmetic) - but sometimes the reflection doesn't want to swap back.
The Wheel That Owes You. A towering game wheel run by a fast-talking barker. Paying 1 gp and spinning grants a random minor boon or debt: a cryptic favor owed to the carnival, redeemable later, or a small immediate reward (a trinket, a song stuck in your head that grants advantage on one Persuasion check, etc).
The Ticket Booth With No Line. A booth staffed by a bored functionary who sells tickets required to leave the carnival and return through the Curtain. Tickets are 'purchased' with a memory, freely given and vividly described, not gold.
Distinguishing features
The ship itself is unremarkable and slow, a deliberate disguise for what it carries
The portal is a canvas curtain in the cargo hold; stepping through takes you to the pocket carnival regardless of the ship's actual location in the void
The carnival's sky never changes and no one inside can agree on how long they've been there
Time inside the pocket plane runs strangely: an hour at the ring-toss may cost a day outside, or an afternoon may cost nothing at all
Inhabitants
Madam Vell, the Ringmaster (fey noble, appears as an elegant woman with a fox's shadow). Gracious host, terrible negotiator's opponent; delights in bargains that sound fair and aren't quite
The carnival barkers and performers (satyrs, pixies, a few willing human former guests who never left). Friendly, theatrical, always selling something
Ship's crew (the captain and two deckhands, ordinary humans/half-elves). Wary and protective of the portal's secret, paid well by Madam Vell to ferry it between ports
Secret
The Ringmaster herself is bound to the carnival - she cannot leave through the Curtain. If a party learns her true name (whispered by a losing mirror reflection, or won from the Wheel That Owes You) and speaks it aloud inside the Hall of Losing Mirrors, she must answer one question with total honesty, including how to permanently anchor the Curtain so the carnival can never move again.