Complex sentence: Sadly he mysteriously vanished in 2016 during a covert expedition within the Iron Mountains in Ireland searching for a Neolithic doorway to an other-world spoken about in an 8th century manuscript recently uncovered in Trinity College, Dublin.
Split into simpler sentences: Sadly he mysteriously vanished in 2016 during a covert expedition within the Iron Mountains in Ireland. He was searching for a Neolithic doorway to an other-world written about in an 8th century manuscript recently uncovered in Trinity College, Dublin.