Le Serpent Rouge. And as we know, the poem is set in the landscape around Rennes-le-Chateau and Rennes-les-Bains. So - the line in the Libra verse which reports 'At the window of the ruined house I gazed across the trees stripped by autumn to the summit of the mountain'.
[A la fenêtre de la maison ruinée, je contemplais à travers les arbres dépouillés par l'automme le sommet de la montagne] where can we find such a ruined house? Could it be indicating a window of the old Chateau [house? It was someone's house in the past!] at Coustaussa? For the old chateau of Coustaussa does have ruined windows which observe a mountain. The mountain of course is Cardou [see image below].
An objection may be raised on the grounds that Coustaussa was never a house, but a defensive castle. But seeHERE where the author feels that the chateau is not wholly defensive but was made for comfort and elegant living. That is, a House!
One can see in this old photo how Coustaussa looks out to a mountain ...one can even see the 'window'gazed across the trees stripped by autumn to the summit of the mountain - Cardou seen from the ruined house in autumn/OctoberI gazed across the trees stripped by autumn to the summit of the mountain - Cardou seen from the ruined house in autumn/October