Science museum. Some stuff is old and worn. But the actual science on display is quite ambitious, you can learn stuff here, although most text is in French.
A nice touch is that several of the labs that were used for research in the olden days are today still in use; scientists in white coats do popular science demos for the kids.
Things to do
You will definitely like Montmartre. It is a village raised up on high, with winding, cobbled streets, and little squares with gardens, which have become petanque grounds, and the warm cafés, former intellectual cafés where philosophers, writers and other artists met to ponder over the Society of their time while enjoying a drink. I WANNA COME BACK!;)
A wonderfull location that you can visit near Eiffel Tower. A great place to take some pictures for your personnal Paris album
