The obverse (Christopher Columbus portrait) and reverse (
Santa Maria with globes/maps of Eastern and Western hemisphere) designs of the 1892-93 World's Columbian Exposition Half Dollars are among the most recognizable of the classic era US commemorative series. This can be attributed to the coin's significant overall mintage, the large number of the coins released into circulation, the popularity of collecting coins that depict ships, its frequent appearances at coin shows and/or the number of modern-era medals that re-create the designs (among other reasons).
1892-93 World's Columbian Exposition Half Dollar

But the ship reverse could have been very different!

In April 1892, ahead of the coin's authorization by Congress, US Mint Director Frank Aleamon Leach commented "...these coins will be of unique design. On one side there will be a head of Columbus and on the other an appropriate inscription." Leach also noted that the coins were to be circulating coins intended to be used as an admission fee at the Exposition vs. sold at a premium by Exposition organizers. Leach was 1 for 3 with these "predictions."

In June 1892, a syndicated press release reported that, regarding the coin's design, "on the one side the administration building at Chicago fronting on the lake, and on the other side a head of Columbus."

August 1892 newspaper reports indicated that designs for the coin had been selected and that they were to feature Columbus on the obverse and the Main Building of the Exposition on the reverse.

A September 1892 press release noted that approved designs for the coin had been received by the Mint, with Director Leach announcing "The Madrid head of Columbus will appear on the face of the coin and the western hemisphere on the reverse." I'll give Leach a 1.33 out of 2 this time out.
It's clear from these various preliminary design notices that a decision to include a portrait of Columbus had been made early in the coin's design development process, but that the design for the reverse was rather fluid - from just inscriptions to the main Exposition building to a map of the western hemisphere.
Many medals, tokens and other items of exonumia were created for the World's Columbian Exposition. The Main/Administration Building would make an appearance on more than one.
In late September 1892, accurate design details began to emerge. It was reported that "The design adopted for the coin is the Lotte head of Columbus for obverse, and a caravel and two globes for reverse." Considering the Mint struck the 1892-dated coins in November and December 1892, getting accurate information in September seems about right for the production timeline!
Curious about the "Lotte head" referenced above, read more about it here:
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Model For Columbus' Portrait On Half-Dollar?For other of my posts about commemorative coins and medals, including more on the Columbian half dollars, see:
Commems Collection.