I marshall the GP every year at Spa, and have done so twice at Monza. We have been able to climb (not walk up )the banking in the week preceding the GP and it is so full of history, you can almost hear and feel the cars thundering around it !! I'm not sure what Ascari is like from a speccy point of view but it was awesome as a marshall, that is one experience I will never forget as they came under the baking and " attempted " to get through the first left hander !! As has been said the Parabolica and also the first chicane are special places to be but then so is the whole circuit, it just leeks history and passion out of every pore.
The same as Spa one of the true great places left to experience in the sport. If you do go to Spa do take the time to go round the old long circuit ( I saw the last GP on it won by Pedro Rodriguez ) who held the lap record in the 917, spent 8 mins in top gear, didn't lift for the Masta kink and went round the slightly banked corner at Stavelot at 185 mph !!!!
Both awesome circuits !