I've heard the rumors for years and finally had time to look into them. Yep, President Roosevelt did use a formerly secret subway station to hide his polio from the public. He's also not the only one who used (uses) it. The article linked below discusses the station's history and links to an older article with several pics of the place. I love stuff like this when it's real (even though the Transit Authority refused to acknowledge it's existence for decades).
http://www.slate.com/blogs/browbeat/...tion_used.html
There are stills from a BBC expose' on the Business Insider website as well. The article on that site isn't as thorough, but the pics do offer some more interesting tidbits to see. That's found here:
https://www.businessinsider.com/amaz...station-2014-5
Apparently, the station inspired the underground scenes in The Amazing Spiderman 2 as well. I remember those now after seeing the movie stills jogged my memory. They're in one of the articles above.