The Milwr Tunnel, was constructed between 1897 and 1957 to drain lead mines (which are now disused) between Holywell and Mold in Flintshire, North Wales.

The tunnel is approximately 10 miles (16 km) long and discharges water into the Dee Estuary. The vendor is responsible for maintaining water flow in the tunnel and have a right to abstract water from the tunnel, which is potentially suitable for a variety of industrial purposes.

The tunnel trends from near the high-water level at Bagillt Flintshire, on the south bank of the Dee Estuary, to Loggerheads near Mold.

From Bagillt the tunnel was driven at a gradient of 1:1000 in a south westerly direction for approximately 2.6km to Herward Shaft, near Dolphin. From Herward Shaft, the tunnel trends southwards beneath Halkyn Mountain towards Rhydymwyn.

The site consists of two principle separate plots, the first of circa 4.54 Acres open land, the second of circa 1.16 Acres open land with pumping station. The holding also includes mineshaft access land at three nearby locations.
Parcel 1 - 4.54 Ac (1.84 Ha)
Parcel 2 - 1.16 Ac (0.47 Ha)
Open Land
Various Uses Considered (subject to planning)

Non Potable Water
Flows: The water flow in the tunnel varies seasonally and has an average of 1.03 m3/s of flow recorded with a maximum value of 5.34m3/s.
Water Quality: The water originates from beneath the Halkyn Mountain and is generally:
High in Aluminium, Iron, Lead and Zinc
Moderately high in Copper, solids and turbidity
Low in colour
Low in Mercury