The hornwork comprises a pair of walls enclosing a triangular courtyard, linking the east wall of the castle with an irregular hexagonal (or heptagonal) structure.
Today it forms a modest, heptagonal plastered building with a mansard roof, whose outside staircase was removed in recent times for the benefit of traffic.
Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings.
