I have never seen those either. Almost look like precast units that were brought out and installed with spacers/ some type of anchoring material. Almost too clean looking to have been formed, poured and hand finished. I dunno. JMO
That's what they are. We have them all over the city and they go in just like stone.
They look like a lot of work to clean. I'd be worried that my butler would leave us if I had him sweep those things all the time...
do snakes hide under those steps?
