My husband and I have each have a 15 day Swiss Travel Pass. We want to book a round-trip cruise on Lake Brienz from Interlaken OST to Iseltwald-Giessbach to Interlaken OST. When I try to get the discount, it asked for customer number. I read that this is for locals with a Swiss Pass. Is it even necessary to book ahead? I don't want to show up and have the boat be full or long waits, if it's possible to avoid.
Thank you!