A large circle is scribed on the floor. In the center of it is a key and a small slip of paper. At the far end of the room is a door with a strong lock. There is a wooden sign standing in the circle that reads, "No Entry Without a Ticket".
The small scrap of paper in the center of the room has written on it, “Admit One”. The circle can not be entered physically, magically, or by tools or weapons, except by those holding a ticket. Only air and strong gusts of wind can pass through the circle. The magic of the circle is also not terribly discerning; writing “Admit One” on a scrap of parchment is enough to fool it.
Instead of a key in the center, you could place treasure or other objects of desire and necessity in its place.
If you'd like to support my work, high resolution versions are available on my Patreon, as well as early access and exclusive content. I also recently published Strixhaven Orientation Day, a Copper Best Selling supplement for the Strixhaven module that makes it easier to run and includes a few puzzling encounters too!
![Admit One - Dungeon Puzzle [OC] [Art]](https://i.redd.it/c0z5wbvx72y81.jpg)
If you'd like to support my work, high resolution versions are available on my Patreon, as well as early access and exclusive content. I also recently published Strixhaven Orientation Day, a Copper Best Selling supplement for the Strixhaven module that makes it easier to run and includes a few puzzling encounters too!