Geograph - photograph every grid square

The Wren's Nest National Nature Reserve is one of the most notable geological locations in the British Isles. It is designated as a Site of Special Scientific Interest (SSSI). It provides a distinct range of limestone habitats with associated species of plants and animals. There are many attractive tracks through the woodland, and by the rock exposures, and geological trails are waymarked.
Over 400 million years ago the area was covered by Silurian coral reefs and tropical seas. This was the environment resulting in the famous fossils which can be found today. Over 700 types are known to have come from Wren's Nest. 186 of these were first discovered and described here. 86 are found in no other rock strata.
Wren's Nest Hill was extensively quarried during the Industrial Revolution for building stone and lime production. The most impressive part of this was the last remaining surface opening limestone cavern in the world – formerly reaching more than 100 metres underground – which is known as the Seven Sisters. These workings were originally connected to a vast underground basin and network on the Dudley No 1 Canal. Quarrying and mining ceased in 1925.
The Seven Sisters caverns had to be filled in after a major roof collapse and mine cave-in (2001). More recent work has also been done, infilling the huge Cathedral Gallery with loose sand.

(Information summarised from Wikipedia and Dudley Council's own Wren's Nest website. There are very many excellent detailed websites available on-line).

Note: Currently (2022) there is only one small and inadequate car park, in Wrens Hill Road. This is locked by the council at 3pm on weekdays and I don't know what time it is opened on weekday mornings. It is locked at all times at weekends.