My idea of penal is where the punishment for a less than perfectly executed shot is excessive. The hole itself may not be 100% penal, but it may have certains design features that are. Take for example a bunker located in a very deep hollow located to the side of or in front of a green. If the recovery shot from the hollow would be considered extremely difficult, then the placement of a bunker in this hollow is penal and excessive in my opinion. I believe you can have a penal element to a hole, even if you have options. I'm talking about the punishment fitting the crime.
I don't consider a long carry over water, rough or some other hazard as penal, as long as you have the option to take an alternative route. I don't view bunkers on either side of the fairway or green as penal, as long as you can avoid them. These type of holes are just tough in my opinion; nothing wrong with tough but fair holes.
Extremely narrow fairways bordered by rough is also penal in my book. I'm thinking of courses with US Open set-ups.
However, if it's a hole where the architect had no other option, but to go with a narrow fairway, I don't consider it penal in the strict sense of the word. One example is the short par 4 9th at Strabane (N Ireland). The river Mourne runs all the way up the left of the fairway and all down the right, a steep bank covered with long grass and bushes awaits the inaccurate drive. In this example, the architect had no option but to go with a narrow fairway.
Yes, I know, a lot of ifs and buts, but nothing is ever black and white.