Like any great city, Chicago is always changing. Familiar landmarks are destroyed. Lost Chicago, by David Lowe, is the classic book on our vanished local heritage.

But what about those well-remembered Chicago oddities that never made the guidebooks, even when they were around? Anyone who’s lived here awhile can come up with several.

For instance, take this picture from 1975.

This structure was located at 6650 West Grand Avenue. A curved driveway, supported on concrete pillars 40 feet above the ground, with no ramps. For most of the thousands who passed it everyday, it was an intriguing mystery. A Northwest Side prototype for the Skyway, perhaps?

The Grand Avenue whatsis was actually a relic of World War II. Built by Western Electric in 1943, it was a track used for testing mobile radar equipment. The location at the top of a ridge made it higher than any buildings for miles around.

Originally a wooden ramp connected the track to the ground. The mobile radar units would drive up to the top, then planes from Glenview Naval Air Station flew over. The data collected was used to determine the efficiency of radar, which was then a new invention.

The track remained in use through 1953 and the Korean War. After that the wooden ramp was removed and the elevated roadway sat unused for over thirty years—it was too expensive to tear it down. This particular landmark was finally replaced by a strip mall in the 1980s.