The first, Kats I Have Known by O. O. Orange (i.e., Keeler), is a chapter [now reprinted as a booklet] he inserted in an otherwise unrelated novel (in which an imprisoned character has to read this essay in order to find a necessary clue to escape) -- one of Keeler's more notable odd practices as a writer. It's an amusing celebration of thirty cats he'd had during his life, from the one who had a pet turtle to the one who protested so vocally at being bathed that the police arrived, nightsticks in hand, to interrupt the foul murder they thought was being perpetrated within.
By contrast, the second, Adventure in Milwaukee is a 'novello' (as he called it; today it'd be called a novella) written in 1916 and then revised in 1922. It's fairly straightforward so far as Keeler goes: a missing brother, a stolen necklace, a monogrammed stiff collar, a mysterious woman on a train, a dashing would-be hero rather out of his depth, a hypnotist who died before making his volunteers wake up, blackmail, multiple mistaken identities, red herrings a-plenty, and much much more. But it's the capturing of a time and place that make it really stand out for me. Having lived in Milwaukee from 1981 to 1992 (and on its outskirts in Hales Corners for another two years after that before departing for the wilds of Delavan), I was fascinated by this glimpse into an earlier Milwaukee. Most of the places the narrator (a stranger in town, hailing from the apparently fictitious small Wisconsin town of Wauwaukauchee Lake, out past Oconomowoc*) visits were familiar to me, so that I could mentally trace his movements. Many were still there when I first arrived: Wisconsin Avenue and Broadway and East Water, Juneau park and Layton Avenue, Clybourn** and Greenfield and 26th street (which I was somewhat surprised to learn was already a run-down, dangerous neighborhood some seventy years before I briefly lived in it, by which time it had become part of The Core).
There were mental adjustments I had to make--the elm trees he mentions as lining 26th street are long gone, of course: my generation and all those younger have no idea what elm-lined streets look like. A few times I was puzzled by the route he was taking, but later I realized this was because my mental map included the interstates, which wd have destroyed many of the obvious surface-street connections from Keeler's time. More importantly, when he mentions catching the 'Wells car' west out Wisconsin, or the 'Oakland car' north to Park Place (on the upper East Side, the neighborhood in which resided the original of Prospero's house in THE FACE IN THE FROST, according to Jn Bellairs), he's not talking about hailing a cab --something he specifically does at another point, calling it a 'bonded carrier' ("bedraggled privately owned automobiles which operated for the nickels of the public") -- but streetcars, a system of which used to criss-cross the city*** (he describes them as "little faded yellow streetcars"). It's only when he has to venture out into West Allis, which he describes as covered with factories (rather than the residential area of my time), that he resorts to hired cars; presumably the public transportation didn't yet extend that far.
Some things had changed greatly between Keeler's time and mine: Gimbels was still a downtown institution when I arrived (I bought a few D&D modules and stray issues of DRAGON there!), but the old train station had already been demolished and replaced by an uninteresting grey shoebox of a Amtrak Station a mile or so to the west and several blocks south (the historic old station was later commemorated with one of the ugliest pieces of public art I've ever seen) and the Pabst Building, once a major local landmark, had been knocked down the year before I came to town, though it was still a familiar sight to me because its image was painted as a faux-'reflection' on a nearby building. The Southern Wisconsin Near-Beer Company, while fictional, sounded just the right note for the era, and I was rather interested to note the occasional nod towards Milwaukee's German flavor, which took a big hit during WWI (there were major anti-draft riots there). No hint of the xenophobia that gripped most of the nation here (e.g., when they made it illegal to play Beethoven): Keeler treats the various German landladies and innkeepers and would-be society figures as mildly comic, such as Herr Hummel, who runs the hotel his hero stays at, the Wisconsin Strasse Deutscher Gasthof.
Strikingly, Keeler never mentions the Milwaukee River without noting the stink, and at one point mentions "three ill-smelling, oily black canals" in what I think must now be the Menominee valley under the viaduct -- they'd cleaned up the river a good deal by the time I arrived, and around 1989 or so opened the floodgates on the Milwaukee itself, which quickly went from a wide, sluggish river to a much cleaner, swifter, more narrow river.
So, here's a little book I'd love to see the Milwaukee Historical Society reprint, with annotations and illustrations, as encapturing a bygone era.
current book: THE SWEETNESS AT THE BOTTOM OF THE PIE by Alan Bradley 
*which is a real place. just so you know, if you're not from those parts.
**though it was surprising to hear an address near what would now be 35th & Clybourne described as a new-build area into which the city had obviously just expanded
***and still continued running into the fifties; my friend Jim Pietrusz still remembers the last of them from his childhood, by which point they had become rather bedraggled themselves through deliberate lack of maintenance.