A manhole is a chamber built on a sewer pipe or conduit usually just large enough for one person to enter.
The manhole provides access from ground level for inspection, clearing of obstructions, or repair.
Manholes are generally found in urban areas, streets and occasionally under sidewalks. They are usually circular shaped to prevent the cover from accidentally falling into the hole.
A manhole cover is often manufactured according to the EN124 norm, which describes the material (concrete or cast iron) and weight classes. For example: a Class D cover according to EN 124 is tested at 40 tons and used in streets with heavy traffic load. This is number 4 in below drawing.
EU Norm EN 124
1: Class A, tested for 1,5 ton
2: Class B, tested for 12,5 tons
3: Class C, tested for 25 tons
4: Class D, tested for 40 tons