CDG airport has showers; I'm aware of showers also at the Gare du Nord, in the McClean public restrooms. I'm sure there are many others, these are just two places that I know have them. Many large train stations and airports are likely to have such facilities nowadays.

I'm curious what you mean by Eurorail? Did you mean Eurostar leaving from Gare de Nord? Or do you just mean another train from somewhere else.
I have seen those McClean restrooms in most of the big stations -- and they look like a great idea as they do offer showers and apparently private changing rooms.

There also is a public bath on rue Oberkampf between the Oberkampf and Parmentier Metro stations that could be an adventure.

To Patrick, by Eurorail, I mean I'm taking a sleeper couchette to Rome from Bercy station in Paris.

There are showers at both Gare Austerlitz and at Gare d. Lyon - - either one is about six blocks. The showers at Austerlitz cost more (does this mean that they are nicer? maybe).

Didn't use either one (and maybe beware of the advice from anyone who HAS used train station showers all over the city, for comparison sake!?) - - LOL!!

Best wishes,

Rex

You could always go for a massage and steambath at the hammam at the Mosquee de Paris at the Arab on rue Geoffroy St-Hilaire, not far from the Bercy station.

Every arrondissement has public baths, usually by its Mairie.

Now that is something I didnt know. I googled and found a list of all of them here:

http://www.paris.fr/portail/Solidarites/Portal.lut?page_id=5458&document_type_id=5&document_id=8972&portlet_id=11757

Looks like you have to bring your own towel.