Shannon Pot is reputedly the source of Ireland's longest river, the Shannon. The River Shannon flows 240 miles south from here to enter the Atlantic Ocean. This is said to be the first place the river appears above ground. This hole has been dived to 16m but it goes much farther underground as there are a huge series of underground caves in this area. Shannon Pot is in County Cavan. It is also now thought that the river may also rise on the nearby Cuilcagh Mountain in Fermanagh but as of now this is the accepted source of the River Shannon.