McDermott's Castle, situated on Castle Island in Lough Key, offers a glimpse into Irish history. Access to the island is typically by boat, either privately arranged or through local tour operators from Lough Key Forest Park. Visiting the castle ruins independently is possible once on the island, though a guided tour may provide richer historical context. Seasonal boat availability might restrict visits during the off-season (typically late autumn and winter). The cost mainly involves boat transport, varying depending on the operator and tour package. A visit to the island and castle ruins usually takes a couple of hours. Note that the castle is mostly ruins, so manage expectations accordingly.