Complex sentence: The line's depot is at Hammersmith, close to Hammersmith station, built by the Great Western Railway to be operated by the Metropolitan Railway when the joint railway was electrified in the early 20th century.
Split into simpler sentences: The line's depot is at Hammersmith, close to Hammersmith station. The depot was built by the Great Western Railway to be operated by the Metropolitan Railway when the joint railway was electrified in the early 20th century.