A functional access port in a machine casing, a machine having a functional access port, and a method of monitoring a machine via a functional access port are disclosed herein. In an embodiment, an access port is provided in the external casing of an industrial machine. The access port comprises a passageway through the external casing of the machine, providing access to an interior of the machine. The access port further includes a removable passageway cover for removably occluding the passageway. A location, a size, a shape, and an orientation of the passageway relative to the external casing are strategically selected in accordance with engineering and design requirements to provide access through the passageway to a desired location on the interior of the machine while the external casing is in place, with minimal to no disassembly of the casing.