I don't know why this scene is so memorable. My older brother and I last saw this movie 30 years ago and we still remember and laugh about this scene when we think of London.
Chevy Chase's laugh/cry moments of utter hysteria and derangement have always made me laugh at/with those scenes even more so as I've gotten older as I can totally relate.
“Look kids, there’s Big Ben! Parliament!”
National Lampoon's European Vacation (1985):
https://youtu.be/iAgX6qlJEMc