Dungeon Starters are for those times when you want to just sit down and start a game right right away. Just a couple pages long, Dungeon Starters provide a unified flavor. Among other things, they include some simple details, questions, impressions, custom moves, items and services, spells and monsters. Sometimes there is even a map or visual image or two.
I've had good experience with The Mines of Fara-Dul from 20 Dungeon Starters. Pretty straight forward and worked well to get a new group of semi-experienced players going.
I made a few myself for convention oneshots that work well. They each consist of an evocative intro paragraph and several leading questions, and sometimes a neat picture.
I'm adding a section about them to Chasing Adventure, and wrote a new one that I'll be using for Dungeon World Day.
You found it! After centuries of rumors and myths, you are the first to lay eyes on the legendary Cloud Fortress. Despite the ancient battle scars covering its surface, the fortress's hull gleams brightly in the sun, its cloak of clouds falling away at your approach. As your hot air balloon softly touches down at the fortress entrance, its edifices begin to pulse with an ominous light.
-What mysterious technology seems to power the fortress (fans, rockets, crystals, etc)?
-What ancient battle did the fortress participate in?
-What terrible foe is it said damaged the fortress long ago?
-What unenviable fate do legends say befell the fortress's inhabitants?
-What powerful weapon did the fortress once make use of?
The important thing for these versions is that the table takes a 5-10 minute break to let the GM prep after character creation and questions being answered.
I really enjoyed "The Paths of Ateşkazé" by Jeremy Strandberg, in Perilous Almanacs. Two of my players (a married couple) are cavers, and they absolutely loved the descriptions of cave passages— they said it felt very realistic, and a couple times they had to tell us a story out of character about their caving!
I've had great luck with Marshall Miller's dungeon starters— they used to be all over the internet but looks like the canonical Google drive source got taken down. Looks like there's some backups here: https://rpggeek.com/rpgseries/22715/dungeon-starters. Several are also included in that 20 dungeon starters book that wunst mentioned, and I also highly recommend. I used a modified version of the Sky Chain as a dungeon in my first DW campaign and it worked great!
As a side note, it's pretty trivial to convert over one-page dungeons (like those from competitions or the amazing Trilemma Adventures https://trilemma.com/ ) into dungeon starter-like prep. Good quality one-pagers tick all the same boxes as good dungeon starters— dripping with flavor, self-contained, and easy to drop in to most settings without much work.