I recently received a letter from a reader who was a dancer at the Edgewater Beach Hotel; she took part in some of the elaborate floor shows performed under the summer stars along the lakefront. She plans on sending in some photos, so I'll post them as soon as they arrive!
For now, you might enjoy this image of the outdoor marble dance floor itself. Many manufacturers of quality building materials at the time would use images of the finished product in their advertising. (I guess that's really no different from today, is it?)
This advertisement for Phenix Marble appeared in Through the Ages, January 1926, p. 50.) It claims that the Edgewater Beach Hotel had the only outdoor marble dance floor in the entire country. The dance floor was directly on the beach, just a few feet from the water — how disappointing it must have been when Lake Shore Drive was extended and the hotel's access to the lake was cut off.