One of the first things we did when we arrived at the Charles de Gaulle Airport was to get two of the 4-day passes from its tourist information center.
We wrote the first day (required) that we used the passes, and for four consecutive days we enjoyed different museums and attractions using these passes. For us, the passes pretty much paid for themselves with the first couple museums we visited. For a couple places that we used the passes, we were actually able to skip lines because of these passes. I loved it.