The Milwr Mine operated along the eastern end of the Milwr Vein, working several mineral-rich branches from the early 18th century. The Milwr Company focused on the most productive section of the vein as it extended eastward from Brynford Hall, eventually intersecting the Holywell-Halkyn Road. By the 19th century, the primary mining site was centered around Milwr Farm, but today, it exists as waste ground surrounded by 20th-century industrial buildings. Larger shafts were historically worked to the southwest of the Halkyn-Holywell Road, north of the farm buildings. Over time, the expansion of the Pistyll housing development has obscured much of the visible mining evidence.

Drainage proved to be a significant challenge for mining operations in the area. A drainage level on the vein still discharges water at SJ 1923 7470, reflecting the site’s long struggle with flooding. The mine faced multiple shutdowns due to drainage issues before the construction of the Sea Level Tunnel in 1904. Initially operated by the Holywell and Halkyn Mining and Tunnel Company, it was later taken over by the Halkyn District United Mines, providing vital drainage to the workings.

Powering the Milwr Mine required significant machinery. When the Milwr Mining Company was established in 1888, it advertised the presence of a compound horizontal pumping engine, which included a 30-inch high-pressure engine and a 56-inch low-pressure engine. By 1893, this machinery was put up for sale, alongside an 18-inch and 14-inch winding engine, as well as a twin 12-inch cylinder capstan engine. Records from 1833 also indicate that a 63-inch pumping engine was in use at the site.