So here’s a weird thing about the subway system here in Porto: it seems to be run on the honour system.  There are no gates anywhere; there are machines to load up your swipe card with the fare for a ride, and there’s these little card scanners around each station that (I think) you’re supposed to swipe before you get on a train and when you transfer, but that’s it.  I’ve never actually seen anyone confirming that passengers have paid their fare. It’s weird.