Where have all the fire hydrants gone?

I was on my deck when I heard a loud noise at the end of our block, like a loud street sweeper. I heard kids shouting too. I went to investigate. Well the city had opened a fire hydrant…where there was no fire hydrant. I didn’t have a chance to look closely but I’m pretty sure the hook up was underground.
A few minutes later they opened another at the other end of the block.
Then I realized I haven’t seen a fire hydrant in years. Why did they put them underground?