Complex sentence: They travelled in the royal train to Barreiro and from there took a boat to cross the Tagus River and disembarked at Cais das Colunas in downtown central Lisbon' principal square Terreiro do Paço.
Split into simpler sentences: They travelled in the royal train to Barreiro and from there took a boat to cross the Tagus River. They disembarked at Cais das Colunas in the principal square of downtown Lisbon, the Terreiro do Paço.