Enter through St John's Gate (13C). The remnants of six crenellated sections of the old wall take you into an open-air area. It is now a popular site (2.5ha) affording pleasant views over the town, the Marne Valley and the Cote 204 Monument. On Bouillon Tower, a stone carved plan depicts the former castle, of great interest to archaeologists. The Château-Thierry "Eagle's Company" takes visitors on a stunning air-borne voyage from the upper courtyard.