Various pictures taken inside TGV trainsets can be found in the European Railway Server's Picture Gallery-- among others, see
Inside a TGV Atlantique trainset, your author standing in the passage between two trailers. As evident in the picture, this is a warm, open, well-lit and quiet place very much unlike the passage between conventional train cars.
Photo by Clem Tillier (firstname.lastname@example.org)
The interior of a first class car in TGV trainset 110, used in the Ligne de Coeur service from Paris to Switzerland.
Photo by Mattias Martensson (email@example.com)