gardens/ruins with wild organics/otherworldly places?

You didn't mention Paris...
But you can go to the Promenade Plantee, or the Coulee Verte.

Think in Chartres the unusual place Maison Picassiette can be of interest for you.

Normandy and Brittany have a lot of public gardens at old estates and farms. A car is essential for these. One of the most famous gardens in France is by appointment only, La Vasterival. See French Gardens, a Guide, by Barbara Abbs, isbn 0-89831-041-5. Most Loire chateaux have gardens, especially Villandry. Have you been to Versailles?

Edit: The Paris Jardin des Plantes is a Metro ride away, but very large and worthwhile in season. See this reference also:
https://www.timeout.com/paris/en/things-to-do/the-ten-best-parks-gardens

Villandry is amazing. It was cloudy and raining the day we visited but I'd love to go there again in good weather. I also thought the gardens at Chenonceau were very nice.

An interesting garden is Le Potager du Roi in Versailles. It is the King's vegetable garden adjacent to the palace and still a working garden, growing every imaginable vegetable and fruit. We booked a tour through La Cuisine Paris, which included transportation on the RER, a guided tour of the garden, a visit to the local market, lunch, and tickets to the palace.

When I read the initial post, I had an idea of the type of garden that I think you want to see and I think that the French, the masters naturally enough of the French Gardening style, do not have a lot of what I think of wild/organics otherworldly gardens. The gardens that I have seen in France, many of which are listed above, are beautiful but are more manicured than I thought of when I read the request. That being said, you may like Parc Villette (Paris) if you like the Sculpture Garden in Grand Rapids. You may like Chateau de Courson in Esonne if you like Wave Hill

If you are passing through the Dordogne department (which I would recommend - it is on the way)) then the gardens at Marqueyssac are not to be missed. Set on a plateau high above the river Dordogne they have magnificent views of the river and the numerous chateaux in the valley below. The gardens are stunning with swirling sculptured boxwood hedging at one end leading to a labyrinth of long shaded woodland paths that take you to the many other features. It also has a café/restaurant that serves simple food and has one of the best views in France.

Also in the Dordogne are the gardens of Eryignac. These gardens are very formal and very 'French'. More importantly they are unbelievably beautiful. Although they are not huge as you walk round them you will realise they are a work of near genius and incredible skill. Once seen they will remain in your memory forever.

They both have websites to wet your appetite.

As mentioned by others the gardens at Villandry are also amazing (though not on the obvious route from Paris to Portugal).

Anyway I am sure you will have a great time.

Nicholas