It's impossible to even count all of the delightful churches worth visiting in Rome (unofficial counts hover at 250), many of which are commonly stumbled on by accident.
Many delightful churches in Rome are found by accident.  
mnli hypothesis: Many delightful churches in Rome are found by accident.   premise: It's impossible to even count all of the delightful churches worth visiting in Rome (unofficial counts hover at 250), many of which are commonly stumbled on by accident.