... and right before your eyes are the most amazing, unexpected things!

The average cast-iron manhole cover weighs about 110 pounds, so they're not really practical as a collectible.
There is however an active and robust group of people around the world who collect and share photographs of
interesting manhole covers. Several examples are shown below:

The most interesting subset of manhole cover art is located in Japan. For about the past 20 years, extremely elaborate,
regionally-themed manhole covers have been created with intricate designs and blazing colors. A dozen examples are
pictured below. If you'd like to see more, Google "fancy Japanese manhole covers" and prepare to have your mind blown!