Outside air to a fan coil unit (FCU)
People normally don't forget to bring outside air (fresh air) to an air handling unit (AHU), but generally Fan Coil Units are not treated the same way. May be because Fan Coil Units circulate smaller amounts of air and designers don't see it necessary to bring the very small amount of required fresh air. But when fan coil units are the only source of conditioned air in a habitable space, bringing fresh air to the FCU is imperative. Ducted return is preferable but in this case the FCU had bottom return and the designer supplied fresh air close to the unit.
Once again in this hotel room scenario the fresh air duct runs in a shaft accessible from the corridor.