KINGSTON, Ont. - Canada's most notorious prison -- dubbed by some as Canada's Alcatraz -- formally shuts its doors today.

The last inmate was transferred out of Kingston Penitentiary in eastern Ontario earlier this month.

Federal officials say the prison, which opened in June 1835, is outdated and too expensive to maintain.

The Lake Ontario-side "pen" has housed some of the worst criminals Canada has produced -- including serial child killer Clifford Olson and Paul Bernardo, who kidnapped and killed two teenaged girls.

It's also been the site of several riots, including one in 1971 that lasted for four days.

Two inmates were killed before the military helped quell the disturbance.

Former guard Mike Dufresne says Kingston Penitentiary exuded a feeling of tension and fear -- while former inmate Lee Chapelle describes the prison as an old rundown dirty "dungeon."

What happens next to the facility, designated a national historic site in 1990, is uncertain.

Some have suggested it be turned into a tourist attraction.

The United Way is capitalizing on the prison's notoriety by holding fundraising tours in October -- with online tickets selling out within hours.