When I travel, I find the 10-24mm and the 18-135mm zooms to pretty much cover everything I want to shoot. You might want to take your 23mm lens for shots in the hotel or boat you may be on, but the 18-135 is my go to lens for its wide range of zoom. the 10-24 is great in older cities where the streets are narrow, or trying to get that shot of a cathedral without having to back up a block. Both of these lens do a great job.