This is a case-study in knowledge representation and dynamic epistemic protocol verification. We analyze the `one hundred prisoners and a lightbulb' puzzle. In this puzzle it is relevant what the agents (prisoners) {\em know}, how their knowledge {\em changes} due to {\em observations}, and how they affect the state of the world by {\em changing facts}, i.e., by their actions. These actions depend on the history of previous actions and observations. Part of its interest is that all actions are {\em local}, i.e.\ not publicly observable, and part of the problem is therefore how to disseminate local results to other agents, and make them {\em global}. The various solutions to the puzzle are presented as protocols (iterated functions from agent's local states, and histories of actions, to actions)