Setting: Italy from about the late 1400s to the present day
So I have two immortals, A and B, and A puts B into a magical sleep while they're in Rome and hides his body (long story). A group of humans in the present day set out to find B so they can wake him up to stop A's evil plan. I'm looking for a place (preferably in or very near Rome, but if you've thought of a really fantastic location for this that's a little bit further away that would be okay too) for A to hide B, but that would also be lightly guarded enough that a few Joe Schmoes (with some magical help, admittedly, but nothing major enough to make getting in and out of a very heavily guarded, heavily-touristed area possible) could get in and steal B's body in the present day without anyone else finding B's body in the span of years between then. The time period the ruin is from is unimportant as long as it existed before about 1480 or 1490, but it would be a nice bonus if the place had some connection to the Catholic Church or Catholicism.
Googled variations on "Italy undisturbed ruins," "Rome unexcavated ruins," and "Italy undiscovered ruins" but kept getting tourist sites, and I'm hoping for something that probably wouldn't be very well-known.