From downtown Saint Paul, Wabasha Street crosses the Mississippi and marches due south until the bluffs force it to jog left. The bluffs here -- deep sandstone beneath a thin limestone cap -- tell some of St. Paul's geological history. Sand piles up where land meets water; limestone, from the deposits of tiny sea creatures, forms in shallow seas. What is now St. Paul was, for eons, the edge of the epicontinental sea that divided North America in two many millions of years ago. The downtown canyon, through which the Mississippi now flows, once held the stupendous glacial River Warren; the bluffs on both sides mark its width and depth. A giant waterfall crossed the river's path thousands of years ago, retreating slowly upstream until it dwindled to nothing. St. Anthony Falls in downtown Minneapolis, now completely artificial, is a remnant.
The soft St. Peter sandstone (named for the St. Peter’s, now Minnesota River) is easy to dig, and small caves were dug to grow mushrooms. Yoerg's Brewery, built into the bluff nearby, dug a mile of caves to store beer, and even advertised the product as “cave aged.” The caves have also been used for entertainment -- the Castle Royal nightclub (1933 -- 1940), carved out dining rooms, a bandstand, and a reputation as a gangster haven during the Depression.
In the 1930s, a professor from the University of Minnesota determined that these caves replicated the conditions of the famous Roquefort caves in France. Thus began an attempt to make St. Paul “the blue cheese capital” of North America. After a faltering start, World War II gave the venture a boost by cutting off imports from France. In 1941, St. Paul produced nearly three million pounds of the stuff. The ex-Castle Royal was the Land O'Lakes cheese cave from 1940 to 1959 and Kraft had cave space too. For reasons now lost, cheese production petered out in the 1950s.
The caves attracted a variety of casual users over the years, particularly, adventure seekers. A series of accidental deaths of young cave explorers – by fire, cave-ins, and three by asphyxiation in 2004 – provoked the city to try to close them all. There have been no deaths since then, but no doubt people still find their way in from time to time.