The Access Code says:
Access rights do not apply to buildings or to other cultural heritage sites where a legitimate entry charge is levied. In other cases such as many unsupervised historic or archaeological sites, access rights apply. These sites can be of great value, though they might not always be obvious on the ground, so it is important to look after them. Follow any local byelaws, regulations or approved guidance asking you to modify your behaviour in order to protect a cultural heritage site.
Leave the site as you find it by: