There are numerous sites documenting the ground we walk on, but my favourite has to be MSRY's Archive of Japanese Access Covers (sewer covers).
You can view the entire archive of 2400+ photos on their Flickr site.
Some similar links:
Written In Stone is a gallery of sidewalks and the stamps and seals left by the people who laid them.
Written in Stone
A gallery of sidewalks, and the stamps and seals left by the people who laid them.
Here's another for Oakland, California:
Oakland Underfoot
fossils in the city’s hardscape
And Denver, Colorado:
Sidewalk Stamps — Andrew Alger
Denver sidewalks are not great. In the next election cycle you can vote to make them better & I hope you do! One great thing about Denver sidewalks are these wonderful little stamps! What a great advertising method. Most stamps I find are decades old. Maybe companies don’t do this anymore. There
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