Originally Posted by
KathyWdrf
It's not clear whether the other posters (above) are actually stating that health club access is strictly an
elite benefit at every Hilton they've stayed at, or simply a benefit to
all guests....

It's an ELITE benefit for Silver, Gold and Diamond members.
From the Hilton Website:
Complimentary Health Club Privileges:
Enjoy complimentary access to the health club or fitness center during your stay, at hotel owned and operated facilities.
It's listed on the Silver tab of the About HHonors page. Gold and Diamond include all the benefits of silver membership, plus the other perks.
http://hhonors1.hilton.com/en_US/hh/about/silver.do