Complex sentence: The railway line that the company built and owned between London and Birmingham, which opened in 1838, was one of the first intercity railway lines in the world and the first railway line to be built into London.
Split into simpler sentences: The railway line that the company built and owned between London and Birmingham, which opened in 1838 was one of the first intercity railway lines in the world. And the first railway line to be built into London.