The King's Crypt

From the introduction:

Welcome to the King’s Crypt, a single encounter adjustable to suit any level of party, though recommended for mid-level characters. In this room, there are several elements for the party to be considerate of, including environmental factors, special effects on a time cycle and even an exit condition. Discovering all of these elements should make the need to pass through this room quickly all the more pressing for your players. This is not a difficult room to complete, but they will need to approach it with haste if they are to survive.