The water tower of Langeoog is one of the island's most well known landmarks.
The water tower provided the island with fresh water from 1909 till 1996. Since then it has been used as an observation deck. Langeoog uses a visitor's tax to run many things on the island. So the admission to the tower is free.
Upon entry you can climb up the very narrow stairs through the tower to the top. Before that you will get a small token. This is, as I said before, no admission fee and you have to return the token later. Once up on top you can admire the great landscape of the island. There is very little room and only 6-10 people fit into the small space on the observation deck. The tokens are used to manage the capacity. As people exit the tower, the tokens are returned and new people are allowed in. This let's the maintainers of the tower keep the tower in good condition and provide a great viewing experience for anyone entering.
And this is when I realized that the water tower was in fact using a Kanban system to manage the flow of visitors in the tower. The system works incredibly well. It does not take into account that 10 adults probably make the room quite crowded whereas 10 children won't, but this is not the point. The point is that by setting the tower's WIP limit (each visitor represents a work item that gets a token) the capacity can be easily managed without introducing heavyweight and costly admission systems.
Langeoog had done it, as you would expect from a small island having to live on limited resources for such a long time. They have implemented a Kanban system and they probably won't even know that they did.