You can simply check-in your flight to CDG, catch a train from the nearby station and get down to central Warsaw for a walk & a meal - perfectly doable, mainly considering that the train only takes roughly 25 minutes (one way). In case the weather is rubbish, then WAW airport is a nice place to spend a few hours. In your case, you've even got lounge access so even better (lounge Polonez for you - not bad at all).

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