[MrJohnston]

It means that if you are going to enter your opponents' secret passage (the one connected to the castle where you are scoring boulders), you may only do so from their courtyard. The same goes for exiting. This rule is designed so that robots cannot avoid the defenses in order to score boulders. You may not use their secret passage to go to the neutral zone.

However, you may go in and out of your secret passage wherever you please.