The Rideau Canal is the oldest continuously operated canal system in North America, and in 2007, it was registered as a UNESCO World Heritage Site. In addition, 24 other National Historic Sites of Canada are in Ottawa, including the Central Chambers, the Central Experimental Farm, the Château Laurier, Confederation Square, the former Ottawa Teachers' College, Office of the Prime Minister and Privy Council, Laurier House and the Parliament Buildings. Many other properties of cultural value have been designated as having "heritage elements" by the City of Ottawa under Part IV of the ''Ontario Heritage Act''.