"A Castellated Monstrosity"
Wilde gave his first lecture in Chicago on February 13, 1882 on the subject of The Decorative Arts lecture in which he included observations about civic beauty and the exterior architecture of buildings.
In his lectures, Wilde often included local references, where possible, and while in Chicago he took the opportunity to comment on Chicago's imposing (154 feet) 1869 water tower which he called "a castellated monstrosity with pepper-boxes stuck all over it".
He was reported as follows:
The Chicago Water Tower
806 North Michigan Avenue, (then Lincoln Parkway) between E. Chicago Ave. and E. Pearson St., Chicago, IL
Built: 1869 (architect William W. Boyington), extant
Current use: Chicago Office of Tourism art gallery
The Chicago Tribune, February 14, 1882.
"I can't help that"
The following day Wilde was interviewed by the Tribune. The reporter put it to him that he had wounded the pride of Chicagoans by slighting the tower. Wilde was unrepentant:
The Chicago Tribune, February 15, 1882.
Victorian Pepper Boxes
Wilde's allusion to the tower's architectural ornamentation was that it was "a castellated monstrosity with pepper boxes stuck all over it".
With this idea Wilde was echoing Hazlitt who said the Brighton Pavilion was “like a collection of stone pumpkins and pepper boxes.” 
 Notes of a Journey Through France and Italy, 1826, ch. 1
Chicago Water Tower and Chicago Avenue Pumping Station, in the 1880s. Lake Michigan visible in the distance.
Despite his strong opinions, the Chicago Water Tower was not the worst building Wilde saw in America. That distinction he was to reserve for the Mormon Tabernacle in Salt Lake City .