The ironstone mine at Port Mulgrave was started by Charles Mark Palmer in the 1850s and was originally called ‘Far Rosedale’ or ‘Rosedale on the Coast’ , it was renamed to avoid confusion with the Rosedale Mines.
The Main Seam at this location is actually slightly below sea level and shafts existed on the shore, but no trace of these remain due to landslips, additional quarrying and underground working of the Top Seam took place much higher up the cliffs and a shaft was sunk to connect to Top Seam workings with the wooden loading gantry on the harbour. The tunnel where this emerged from the cliffs is still visible.
The gate is now securely locked and the tunnel cannot be entered, I took the following photos back in 2007 when it was not locked, they show the large roof collapse just inside the entrance
The brickwork of the tunnel is almost built directly into the cliff face.
The tunnel inside was extended in the 1870s to connect to the Grinkle Mine also owned by Charles Mark Palmer via Dalehouse.