Grain Tower Battery is located on Grain Spit, a mud flat at the east end of the Isle of Grain, opposite Sheerness. The Tower is accessible by a causeway at low tide but at high water it can only be reached by boat.

Grain Tower was completed in 1855 and is similar to the earlier east coast Martello Towers, being externally roughly circular but flattened on the east and north west sides. Internally it is circular. The tower has a slight taper towards the top. Externally it is built of granite blocks while inside the construction is of brick. As with the early Martello Towers, a central circular pillar rises from ground floor level to a vaulted ceiling above the first floor. The entrance is at first floor level with a doorway set into the north west side of the tower.

The entrance opens into a small lobby from which brick vaulted stairs go up in two directions within the thickness of the wall. Ahead is a room with the lower end of the ammunition hoist.

The roof is accessed via a granite staircase in the west side of the tower running between the brick inner walls and the granite outer walls. The original gun positions (one 56 pound cannon and two 32 pound cannon) would have been on the roof but later alterations have removed any original features.

The first remodelling of the tower took place between 1910 and 1912 when two 4.7" Quick Fire guns were relocated to the tower, to fire on high speed torpedo boats attacking ships moored at Sheerness or Chatham. To provide room for the emplacements the tower's parapets were removed and a 2 level crew accommodation block was built. Direction finding equipment and a crew room were added on the roof.

The tower also formed an anchor point for the Medway Boom running across to Sheerness. A heavy chain still wrapped round the tower is the remains of the boom. Wooden posts sticking out of the tower around the chain on the east and west side are the remains of staging used in connection with rigging the boom.

The base of the tower is covered at high tide. There is a causeway across the mud flats. This is uncovered for a couple of hours either side of low tide. The causeway is in moderate repair, but there are some gaps and the whole thing is sometimes covered in some mud. Walking boots, old shoes or wellingtons are recommended.

There is a vertical climb of about 9 or 10 feet from ground level to the first floor entrance. I have visited the tower on numerous occasions. Sometimes there is a rope or a rickety ladder, other times I had to scramble up as best I could. Provided you are quite agile this is not unduly difficult, but it's more than a walk in the park. The location is very remote and you might consider letting someone know where you are going, in case of accident.

The cache is a pill pot about the same size as a 35mm film can, but sturdier. It is covered in black duct tape.

There is a Groundspeak cache at the top of the tower, and another OpenCache at pretty much exactly the same co-ords but separated by a significant vertical distance - one at the bottom and one at the top of the ammunition hoist.

Parking is available at N51 27.198 E000 43.155