We stayed in the "Terriers" treehouse for one night and had a fantastic experience.
We accessed our room using a zip line that took us zooming through the trees and we left by a slightly different one. From the top of our ancient oak tree, we had a terrific view of the forest on one side (badger dens far beneath, owls and squirrels outside the window), on the other side endless fields over which the sun sets.
Dinner and breakfast were delivered in baskets that you pull up via a pulley and we enjoyed ours in the "silence" of the forest on our terrace. We didn't take this option, but you can also ask for champagne, cidre and plenty of other local delicacies.
The treehouses are designed to be 100% eco-friendly and complement the forest rather than damage it. The managers have owned the woods for generations so their priority is to keep them healthy and alive. Your house therefore rests (securely!) on carefully chosen branches without ever piercing the tree's bark.
The woods are also wonderful to go walking in before the sun sets or in the morning after breakfast.
Judging by the guestbook in the room, everybody else who had stayed there before us had loved it too.