Complex sentence: The canals that opened in 2014 are frozen for skating and other winter activities by an underground refrigerant plant in a rebuilt sub-basement that was part of Memorial Auditorium, and a marker on the canal ice denotes center ice's former location.
Split into simpler sentences: The canals that opened in 2014 are frozen for skating and other winter activities by an underground refrigerant plant housed in a rebuilt sub-basement that was part of Memorial Auditorium. In addition, a marker on the canal ice denotes center ice's former location.