Eight Hundred Years of Light

The light

Hook Head is the oldest working lighthouse in the world. The tower you see was built between about 1200 and 1230, on the orders of William Marshal, Earl of Pembroke, whose family had acquired the peninsula. The site had a monastic beacon before that — the monks of Rinn Dubháin kept a fire on the headland from the fifth century, and the local name for the headland, Rinn Dubháin, is where the word "Hook" comes from by way of a Norse-influenced contraction of dubhán, a word for the fishing hooks the monks used.

The tower is not the original Norman structure in every detail. The massive walls are, but the lantern and the gallery were rebuilt, the tower was heightened, and the whole thing was re-equipped in the nineteenth century and again in the twentieth. What has not changed is the position and the function. There has been a light on this headland for something close to fifteen hundred years.

Why the wall is here

The cache is not in the lighthouse. It is at the base of the boundary wall running south from the lighthouse compound, on the seaward side, where the wall protects the approach path from the worst of the weather.

The wall is coursed rubble of local limestone, roughly a metre and a half high, with buttresses at intervals. It is a working wall rather than a decorative one: this headland takes the full fetch of the Atlantic, and without it the path is impassable in a westerly gale.

The find

The container is a magnetic micro, so no compass reading is needed to locate it despite what the hint says. From the second buttress south of the compound gate, walk eight paces south along the seaward face. The container is at the base of the wall, in the shadow line where the bottom course meets the ground, held by a magnetic strip.

The wall is a protected structure and the headland is a Special Protection Area for seabirds. Lift the container out rather than moving any stone. There is no pen in it; bring your own.

The rocks under your feet

The limestone here is Carboniferous, about 340 million years old, and it is packed with fossils. Look at any freshly broken surface along the wall or the shore platform and you will see crinoid stems — the little circular discs that look like washers, sometimes stacked into short columns. Crinoids were sea lilies, animals rather than plants, and they grew in dense meadows on the Carboniferous sea floor. The discs are the individual plates of their stems, and they are the commonest fossil in Ireland.

Access and safety

• The shore platform below the lighthouse is slippery and the sea reaches it in any swell. Do not go down in a westerly or south-westerly wind.
• The headland is exposed; there is no shelter between the lighthouse and Slade harbour.
• The lighthouse is a working aid to navigation. Do not interfere with it or with any of the equipment in the compound.
• Seabirds nest on the cliffs from April to July. Keep back from the edge.

After the find

The Slade harbour walk east gives you a small Norman harbour and a rocky shore that is better for fossils than the tourist beach. The lighthouse visitor centre does tours of the tower, which is 115 steps and worth every one of them in clear weather.