Complex sentence: Ottawa's Union Station, built in 1912, a year after Penn Station, is another replica of the Baths of Caracalla; its departure hall now provides an idea of what the interior of Penn Station looked like (at half the scale).
Split into simpler sentences: Ottawa's Union Station, built a year after Penn Station (in 1912), is another replica of the Baths of Caracalla. This train station's departures hall now provides an idea of what the interior of Penn Station looked like (at half the scale).