A row of three identical World War 2 section posts can be found along the edge of the Seal Sands nature reserve.
The most northerly is open at both ends, although its view has been blocked by a later bank, internally some concrete shelves remain along the walls.
The central post is similarly blocked by a large bank.
The most southerly post retains its outside views although some attempts have been made to block the doorways.
Due to land reclamation they are now inland, but would have overlooked a much larger Seal Sands during World War 2
The entrance can be easily located by crossing the stepping stones near the old mill and travelling towards the viaduct on the south bank
The brickwork around the entrance is under attack from the trees
Inside the tunnel is in good condition, although muddy. The dark red line on the side suggests it may have been deeply flooded at some point in the past.
In the stream outside there is a row of bricks with some discoloured water leaking out, perhaps some sort of drain from the drift.
This drift is a failed drainage level for Longacres mines.
The trackbed of a railway can be seen on the map, running from Swainby directly up to the mine entrance, what appears to be an old rail carriage is being used as a shed near the roadside.
Following the direction of the track a short distance into the woods leads to the mouth of two small tunnels.
One tunnel was for ventilation and the other the main drift, both are full of water and filled with earth a very short distance in.
There are a number of depressions behind the tunnels where the workings have collapsed, the remains of a ventilation shaft are marked higher up the hillside, a large spoil heap without vegitation is also very prominent.
The ironstone mines operated from 1857 to 1887 in this area