Intriguing….
The numbers look new so I imagine whatever it held originally has been replaced by something modern, such as part of the street-lighting system as others suggest, possibly not even related to its first use.
Does the dome look as if it supported something rising higher, such as originally a street-lamp, electric or gas? Or is just a raised roof that gives/gave internal clearance for the mysteries within?
I wonder why someone has carefully painted just the side, and possibly not long ago?