Day hikes near Paris?

Hello. I'm headed to Paris and Toulouse (for a friend's wedding) for a week soon. I used to do a lot of walking in rural France on the Grande Randonnee trails when I was younger, and I love the mix of villages, woods, old castles, etc.

I will have limited time but would like to get some good day hikes in near either Paris or Toulouse, ideally with a rural - countryside feel. Back in the day I used to buy FFRP guidebooks at bookstores in Paris but it appears the bookstore I went to for this (the IGN bookstore) has closed now. It is also very hard to get guidebooks in the US.

Does anyone have suggestions either on:

1. Particularly good day hikes to do from Paris or Toulouse? We will not have a car so the start needs to be train or taxi accessible (ideally train).
2. A bookstore in Paris where I can still buy good hiking guidebooks?

I speak French but it's rusty.