 This means that the only readily accessible route to the castle lies to the east, where the ridge slopes more gently.The defensive advantage of such a site is clear, but the geology of the rock also presents difficulties, since basalt is an extremely poor aquifer.Providing water to the Upper Ward of the castle was problematic, and despite the sinking of a deep well, the water supply often ran out during drought or siege, for example during the Lang Siege of 1573.