Lough Key  Lough Key () is a lake in Ireland. It is in the northwest of County Roscommon, northeast of the town of Boyle. The lough is believed to be named after a mythical figure named Cé. The name "Lough Key" comes from the Irish "Loch Cé". In Irish mythology, Cé was the druid of the god Nuada. He was wounded in the Second Battle of Mag Tuired and fled southward until he came to Carn Corrslebe, where he rested. He saw ahead of him a beautiful plain full of flowers. He sought to reach it, and when he did, he died. When his grave was dug there, a lake burst out of it, and flooded the whole plain. It was thus named Loch Cé after him. The lake is in the northern part of the River Shannon drainage basin, and is fed by the Boyle River which flows from Lough Gara, through the town of Boyle, into Lough Key. From there it flows eastwards until it reaches the River Shannon just above Carrick-on-Shannon. Its area is and its average depth is . One can see a view of the lake from the N4 road as it ascends the Curlew Mountains after bypassing Boyle. The view is enhanced by a modern steel sculpture of an Irish chieftain mounted on horseback (see photograph). The area around Lough Key and the nearby town of Boyle, in County Roscommon, have been inhabited for thousands of years. The lake is several kilometres across and contains over thirty wooded islands including Castle Island, Trinity Island, Orchard Island, Stag Island, Bullock Island, and Drumman's Island. Castle Island has had a number of structures built on it over the centuries. The earliest record dates to 1184, in the Annals of Loch Cé, where a lightning strike is reported to have started a fire in "The Rock of Loch-Cé," a "very magnificent, kingly residence." Currently a folly castle built in the early 19th century by the King family stands on the island. Trinity and Church Islands each have the ruins of medieval priories standing on them. The King family acquired the land around Lough Key in the 17th century Cromwellian Settlement, renaming the area from Moylurg to Rockingham. In 1809, Rockingham House – a mansion designed by English architect John Nash – was built. The house remained the seat of the Stafford-King-Harman family until it was badly damaged in a fire in 1957.