I realize my comment gave perhaps an inaccurate impression, but even with an incredibly sparse itinerary, and bounteous amounts of time (I spent weeks in Italy. I went through Belgium and France over two weeks. I spent a day just wandering around Paris with no itinerary, in addition to days more doing a variety of things), being completely inundated with new and unknown -- even the most benign door or building -- added to staying in a strange places, eating at strange places, and being detached from your normal life, for me at least made the experience far less...persistent.
The Sistine Chapel experience, for instance, aside from being just a mass of people being shuffled through one of the largest tourist draws in the world, was on a day that started with incidentally seeing Pope JP2 give an address, and ended with seeing the Dalai Lama at Tivoli when going there for a dinner (two spiritual leaders in one day! Yet I remain an agnostic). In the end the Chapel got filed away as "neat some stuff painted on a ceiling". That is an extreme example, but for my "a 100 year old is historic" North American sensibilities, virtually everything in places like Belgium, France and Italy is overwhelming, from the weird little waffle shop in Ypres to the sound of bells, the stones on the street, etc, everything just becomes an onslaught of overwhelming experience.