What about Monaco? There’s a whole host of choices for that. Fisi’s in 2005 was quite big, and Brundle’s in 1984 was bad as well. Then there’s the huge start line pile up caused by Derek Daly in 1980, and Jenson’s massive shunt in practice in 2003 which meant he couldnt start the race.
There was also a colossal shunt in the 1950 race when a freak wave soaked the track and caused a massive pile up, and who can forget when Ascari plunged into the harbour in ’55.
And though it wasn’t particularly destructive, but when Brabham crashed out of the lead on the last corner of the last lap in 1970 it must have been pretty bad for him!