This looks so fun. Unfortunatley it says:
Other than the guided walks, there is no public access to the Dungeness mirrors, which are in the middle of a disused gravel pit. It used to be possible for trespassers to gain access to the mirrors, but this is no longer physically possible. The deep lake created by gravel extraction has been extended to completely surround the mirrors, which are now on an island. The only access to the island is via a swing bridge, which is locked in the open position when not being used for guided walks. The good news is that this should keep out vandals and undesirables!
Most of old site should be working now so if you find bits that aren’t let me know in the book. Theres quite a few new things on the right.