[Breschau]

I've not tried it much, but you can preach while 'stealthed' in an enemy province. However, according to the descriptive text, you're more likely to be detected preaching than if you were just sitting there or passing through.

I tested it in a (demo) game just now - had a Machaka Ear of the Lord (Stealth (+10) and holy 2) - preached in an empty enemy province for several turns, and been preaching for 2 turns now in a province with 50 satyrs in it (AI nation rather than indie).