[lnanek2]

Don't forget that things aren't the same everywhere. The land in Alaska and New York is rising pretty fast, geologically speaking, since the weight of glaciers came off. Meanwhile New Orleans is sinking. Chicago took matters into their own hands and raised street level an entire floor to combat flooding. We still have ancient caves at ground level in New York, but I'm sure stuff buried under a city survives better.

[Piskvorrr]

"raised street level an entire floor to combat flooding" - yup, that's pretty much the same technique by which "the ancient cities are rising." Except that Chicago was lifted up, whereas the old cities were only readjusted - essentially, ground level becomes the first basement, entrance is now on what used to be second floor. This process could be repeated, giving rise to old ground-level floors becoming the third basement or similar. Case in point: Prague's Old Town, founded at riverside, was gradually raised by up to 30 feet (which has unexpected consequences, and actually worsens the flooding problems it was always expected to solve).