Getting from Paris TO Lourdes

I will be spending about 10 days in Paris this summer with my 87 year old mother. She wants to go to Lourdes to see the Grotto. I knew to know the fastest way to get from Paris to Lourdes, either by plane or train. I would like to do the trip in one day, leaving Paris in the morning, get to Lourdes, look around for a few hours, and then head back to Paris. ANYONE HAVE ANY IDEAS ???