Complex sentence: Increasingly, especially in the 20th century, Mainz also began to be used as a starting point or stopover location for Rhine tourist cruises, especially of the'Romantic Rhine' of castles and cliffs, being mainly the stretch between Mainz and Koblenz.
Split into simpler sentences: Increasingly, especially in the 20th century, Mainz also began to be used as a starting point or stopover location for Rhine tourist cruises. These excursion mainly visit the stretch of the river known as the'Romantic Rhine' of castles and cliffs, being mainly the length between Mainz and Koblenz.