Halwyn was a small nineteenth-century opencast iron working near the Mount and Treamble group of mines. Its place in the Great Perran Iron Lode landscape is easier to understand from the map than from a surviving engine house: an opencast mine could leave a pit rather than the familiar chimney-and-engine-house silhouette.
The neighbouring Mount and Treamble entries show how several separate properties worked the same mineral belt. The mapped position is the historic locality, not a visitor entrance.
Where it is
Halwyn Mine / Halwyn Pit
50.366291, -5.129595 · Position source: https://webapps.bgs.ac.uk/memoirs/docs/B01793.html
Historic mine locality from the Geological Survey grid [SW 77530 56505]; not a surveyed shaft or visitor entrance
Visiting and access
A location reference, not confirmation of public access or a visitor entrance.
Sources
Source: https://goonhavern.com/mining/ Source: https://webapps.bgs.ac.uk/memoirs/docs/B01793.html