Yes, you can do some rock climbing while on a cruise. All the Royal Caribbean ships have rock climbing walls. No, they aren’t all the same, but if it’s something you enjoy, you can do so without additional charge while on any of the ships.
This wall is on the Symphony of the Seas. You get to it from the Boardwalk (an experience in itself) right outside the Aquatheater (another fun experience).
Whoever said there was nothing to do on a cruise ship hasn’t been on a cruise ship, or at least lately.