Oh dear! The ground collapsed north of the main post office in downtown a couple of weeks ago.
There are many things down there, including the old cellars of the Julius Winkelmeyer Brewery, which dated back to the 1840s (and used to frequently beat Adam Lemp out for first place in the city’s fair every year for best lager beer). This was not some “also ran” brewery but rather one of the most important in the city for decades.
While the brewery was demolished in around the turn of the Twentieth Century, the cellars remained underneath it, including the branch that extended north under what is now the Gateway Mall. I think these parallel passageways are the seed of truth that gave rise to the absurd myth that there were once tunnels that stretched all the way from this area to Uhrig’s Cave at Jefferson and Washington avenues.