I went on a cruise and accidentally locked myself in the ship's library.

This joke sails smoothly into humor thanks to a clever bit of wordplay and a dash of situational irony. The setup paints a picture of a mild predicament: being accidentally locked in a ship's library. The punchline, "I guess you could say I was stranded with a good book!", then playfully twists the common understanding of the word "stranded." Typically, being stranded implies a dire, isolated, and often dangerous situation, like being stuck on a desert island or lost at sea.

However, a ship's library, while perhaps a bit confining if locked in, is hardly a life-threatening scenario. It's usually a cozy, quiet space filled with intellectual treasures. The humor comes from applying a term with such high stakes ("stranded") to a relatively pleasant, low-stakes situation. Cruises themselves are often seen as escapes from the everyday, a chance to relax and enjoy amenities, and a ship's library is just one more way to unwind. The joke cleverly subverts our expectations, turning a potential minor annoyance into a chuckle-worthy observation about finding the silver lining, or perhaps, the silver binding.