Crews with the Milwaukee Metropolitan Sewerage District are checking a section of the rainwater and sewage holding system more than a hundred feet below the ground.

Three people made their way 135 feet underground.

They are checking up on a portion of the deep tunnel - the system which holds excess water during rainstorms.

These engineers check up on the deep tunnel every 10 years using advanced cameras and transportation.

The segment getting checked out is seven miles long.

They ride a piece of equipment that looks almost like a buggy on it sits a driver, a camera person, and another person documenting what they see.

They also take with them plenty of oxygen.

They are looking to see if there is any sediment build up or if any sections of concrete need to be replaced.

While underground those engineers will be in complete darkness.

The equipment is thoroughly checked beforehand in the interest of worker safety.