Exactly. Anything that is known to exist is now protected by the appropriate government, and anything that is open to the public has been made tourist-proof to some extent.
I was very fortunate to spend a semester in Rome when I was in college, and we got a lot of access to sites through the program we were in that are not generally available to the public.
So the interiors of Etruscan tombs, Nero's "golden house" which is largely underground now, the various catacombs, the Roman ruins under St. Peter's (including something that may or
may not be St. Peter's actual tomb), etc. etc. And my dear friend Art had a notorious fondness for breaking the rules and sneaking off into places where we weren't supposed to be,
and sometimes he managed to lure me into accompanying him. This was either extra-curricular intellectual inquiry, or, um, unlawful trespass. :whistle:
We use to just say that Art's area
of research was Roman sewers. But basically, in Italy in the late winter and early spring, everything underground is cool cool cool. Might get hot in the summer.
But yep, as you say, most things accessible (legally) to the public are just big hunks of rubble now. The first three pics below are from the Tomb of the Scipios, which is 2000+ years old, but
ultimately no more or less significant than, say, Grant's Tomb or Monticello. Fourth is a good example of 20-year-olds' sense of archaeological research and intellectual inquiry, after a long
morning involving a lot of hiking, when everyone just wanted to turn their brains off, lie in the sun, and eat lunch. I had just given the oral version of my term paper for the semester at a
nearby temple, and then we went over to the remains of a theatre - this is in the middle of nowhere in Sicily.