This is a work from my 'manhole cover-project'. I collect photos of manhole covers from various towns and villages in Europe. This one is located in Frederikssund in Denmark. A manhole cover shuts off a well and is usually made of heavy metal. In general old covers are square, whereas modern ones are round. Whatever form they have, all lids are embossed to create grip. The reason for the switch from square to round was that a round manhole cover will never fall into the pit. A square one could (diagonally/vertically) fall in its own pit and that would be life-threatening for someone working in the shaft. In addition, round lids weigh less than square ones with the same diameter. Despite of the fact that the manhole cover itself may be round, the iron frame around the pit is almost always square to fit with the paving around it. Round frames are only used if the well is laid in asphalt. When cars drive over a manhole cover, it should not be lifted up by vibrations. But a race car is pressed so strongly against the surface of the road by its aerodynamics at high speed, that low air pressure occurs under the car, which is strong enough to lift a manhole cover. So in street races with formula-1 cars manhole covers are usually firmly welded.......Well, well, well, we might conclude that there’s a lot to learn about manhole covers☺!