While at the gite in France, we took just one day trip (we basically spent two weeks sat in the shade of a large oak tree, reading) - this was to the "Jardin des Nenuphars", Latour-Marliac, at Le Temple sur Lot, a few minutes from Villeneuve-sur-Lot. This is where hardy waterliliy hybrids were first grown and from where Monet bought the lilies for his garden at Giverny. They house the French national collection.
A lovely place, really interesting (and with a good cafe), although the greenhouse containing the exotic/large lilies was unbelievably hot and humid - it took me a fair while to recover from just a few minutes in there!...