Which disaster almost destroyed London in 1666?

In 1666, a fire swept through London, destroying 13,200 houses, 87 parish churches, The Royal Exchange, Guildhall, and St. Paul’s Cathedral. The Great Fire of London started on Sunday, 2 September 1666 in a baker's shop on Pudding Lane belonging to Thomas Farynor (Farriner). Although he claimed to have extinguished the fire, three hours later at 1 am, his house was a blazing inferno.

Source: London Fire Brigade