Location: View location on map Status: Turned into park (but there is an abandoned section) Access to site: YES
Grain Fort and Wing Battery are located on the shore oppersite the sea fort. This places has been turned into a park and not much of the fort still remains. There are two sets of underground tunnels under this fort. I managed to find the entrance and got into the south tunnels, but have not yet managed to find the entrance of the north tunnels.
Here are the south tunnels. These tunnels are a few hundred meters long. Getting in to these tunnels involves wriggerling though a very small narrow hole only just large enough to get through. Once inside the tunnel it is about a 200 meter walk until you get to the large boiler blocking the way, then after passing the boiler is the junction. There are two route off the junction, turning right leads to where someone has bricked up the route leading to the north tunnels, and turning left leads to where the tunnel has been filled in with soil.
In the north tunnels there is even more to see, but I havn't been able to get into these.