Manhole

Opening to a confined space

A manhole, also called utility hole, maintenance hole, or sewer hole, is an opening to a confined space such as a shaft, utility vault, or large vessel. Manholes, typically protected by a manhole cover, are often used as an access point for an underground public utility, allowing inspection, maintenance, and system upgrades. The majority of underground services have manholes, including water, sewers, telephone, electricity, storm drains, district heating, and gas.

From Wikipedia, under CC BY-SA. More on occurri.