anyone know if there is a place to buy a shower in the charles de gaulle airport in the middle of the day - other than renting a room at the sheraton?

If you are arriving or departing on UA (in business or first) or have access to the Red Carpet Lounge, the CDG RCC has quite nice showers to use for free.

Another option is a day room at a CDG hotel like the Mercure (not on-site of CDG).

Another option is a certain Ibis hotel that can be accessed by the free ADP bus around CDG. It rents rooms with showers for €10-12 per hour. I've posted about it here before.

I'll run a query and come back with the link.

http://flyertalk.com/forum/showpost.php?p=4023219&postcount=2

Courtesy of PHLFlyer:

- clear passport control
- hop on the ADP airport shuttle #5 to "Terminal 3/Roissypole"
- the bus stops in front of the IBIS hotel at Roissypole where you can get a room at 10 euros per hour between 10am and 6pm (note: there are several Ibis at CDG; look for "Ibis Paris Charles de Gaulle Aéroport-Gares").

If you can skip the transfer desk and have a short wait at passport control you should be able to get to the hotel within 30 minutes of arrival. This will give you a good hour to use the room before you head back to your boarding gate. The shuttles run every 7 minutes and the trip is usually quick. There are also some spots to pick up coffee, etc. in the lobby or just inside the train/bus terminal.

http://www.flyertalk.com/forum/showpost.php?p=3814505&postcount=2

Hope that is helpful to some others here.

There is one public shower in each of the restrooms at the RER station. They ask a user to leave an ID with the station kiosk attendant to get the key.