New Hampshire circa 1900. "The Wizard Tree, Cathedral Woods, North Conway, White Mountains." 8x10 glass transparency, Detroit Publishing. View full size.

Washington, D.C., 1923. All it says here is "Dept. of Agriculture." Back when the place was run by the Keebler Elves. National Photo Company. View full size.

Orchard Lake, Michigan, circa 1900. "Cavalry detachment, throwing horses. Michigan Military Academy." Detroit Publishing glass negative. View full size.

Circa 1908. "Mr. and Mrs. Frank Kern and trained dog Bobbie." 8x10 inch dry plate glass negative, Detroit Publishing Company. View full size.

Washington, D.C., 1917. "Reynolds, J., performing acrobatic and balancing acts on high cornice above Ninth Street N.W." Our fourth glimpse of "Jug" Reynolds at work atop the Lansburgh furniture store. Harris & Ewing. View full size.

My great-granduncle George Richardson Jr., Denver, Colorado, ca. 1897. He was pretty into trick photography as a young lad.View full size.

September 26, 1924. Washington, D.C. "Mysterious tunnel." A strong Hardy Boys vibe here. National Photo Company Collection glass negative. View full size.

UPDATE: While initial speculation (bootlegging, espionage) was soon dispelled by an eccentric insect expert's explanation that he had dug the passages "for exercise," historical evidence suggests that this was a tunnel of love. Or at the very least, bigamy.