I have the same question with Hyatt and SPG... I would love a place to shower before work, as I plan to start biking there a bit.
there are Westin workout locations that have weight room, spin classes and a locker room/showers that allow monthly access or a 20 visit pre-pay. I did it with the SPG card, so it earned points, too. They have workout clothes and lockers on site, so no need to carry much in. Call your location and find out.