The Castellia Mines is a system-neutral adventure about the forsaken property of a decadent noble family.
It's 6 pages, with an old-timey document aesthetic to its layout, and some great, atmospheric images.
Content-wise, Castellia has you surveying some old mines belonging to a (now mostly dead) family. There aren't any serious swerves to the investigation---you fight the things you'd expect to fight in an old mine---but there's combat and loot and history to uncover, and the writing is solid and expressive.
The runtime for Castellia is potentially pretty short (depending on how much prologue you include before the party reaches the mine,) and the adventure should fit neatly into a one-shot or convention game time block. It also makes an easy jumping-off point for a campaign of helping a noble heir flip other haunted properties.
As a system-neutral adventure, Castellia pairs very easily with DnD (any edition.) It's a heroic fantasy with gothic tones and periodic combat, and that's DnD's bread and butter. OSR also feels like an easy match, although Castellia doesn't get especially weird or dark---it's played pretty straight---so something like Brighthammer might be a good pick. Blue Rose could be another good choice, especially if you want to dwell on the character drama---and all of these systems should be able to handle Castellia with minimal conversion work.
There's also no reason you couldn't run it with something further afield like Symbaroum or Shadows Of Esteren.
Overall, if you like heroic fantasy, combat, and a little bit of spooky atmosphere, and if you're looking for a quick, direct adventure, Castellia Mine should be on your list of scenarios to check out.