Sanctuary of Belches is designed for four 5th-level characters. Let’s read!
This adventure has the sort of convoluted lots-going-on setup that makes me think of the stereotypical Dungeon Magazine adventure. Short version: duergar excavating a temple unearthed some magic items that have resulted in their leader being possessed and a giant they were employing to be obsessed with a magic horn. Now the belching giant is locked within, orcs attracted to the magic horn are swarming outside, and… yeah. Ostensibly your hero-goal is to eliminate the horn. Underlying theme is the reawakening of a horrible eldritch spirit called Youm, who is into death and cold and worms (swipe right!)
There’s an interesting on-the-way encounter with two frost fey and a yeti that leads to more frost fey stuff, but this feels kind of like an add-on intended to introduce the PCs to the idea of the rime-worms that come up later, and an opportunity to get magical earmuffs that protect (somewhat) against the enchanted horn.
When the PCs arrive, orcs are besieging the temple and fighting the duergar and their flab giants (love it). There’s too much going on for PCs to attack everything - the module tells us as much - and then midway through the combat, two warriors with inclusive backgrounds arrive in a wolf-drawn sled and add to the chaos. This pair, if they survive the battle, have good intel to share with the PCs.
The actual temple looks like a pretty nice delve. Lots of duergar, rime-worms, the constant threat of the giant’s toxic belches befouling the air everywhere, and some other challenges and situations here and there to keep it interesting. Some good combat-scene setups for the tactically-minded.
The adventure presumes that PCs will attempt to parley with the duergar at some point and team up to deal with the Other Stuff Going On. I think this assumption is wedded to the idea that you’re running four fifth-level characters. A larger, more experienced, more foolhardy, or more daring group might say “screw it” and try to wipe the whole place. The duergar are behind some impressive barricades but there are only eight of them; what party isn’t going to attempt to chuck a fireball back there?
The duergar’s leader has gone bug-nuts, possessed by a lingering icy spirit of the temple. If the spirit is driven out of her, it can attempt to possess one of the PCs. Nice!
There are magic trap/effects to deal with on the way to the sanctuary where the belching giant is holed up. These provide a break between combats and are sufficiently interesting to be worth the time. There’s also an earth elemental to deal with.
Undead fight, because why not. At least they’re some interesting types.
Finally, the confrontation with the belching giant who’s been eating all these awful magic rime-worms. The potential sequence of fighting this giant (with magic deafening horn) and then the avatar of Youm itself, seems pretty cool. There’s a lot of poison damage going on here. If you were going to escalate this to an old-school adventure, consider carefully which poison effects are going to nauseate or do direct damage, and which ones should be elevated to save-or-die.
All in all, this is a decent adventure setup with some nifty bits. It’s difficult for me to gauge how long it would take to run; it would definitely benefit from being grounded in other general adventures in the wilderness region around the temple, so maybe this is something you could drop on the map and see what happens. I’d also consider tying it to some other worm-forward adventure, like DCC’s Well of the Worm.