One of the great things about fantasy games like Pathfinder is the sheer number of different styles of adventuring that are possible. There's a lot more than just dungeons and dragons (pun intended). You can explore the wilderness, journey through tangled jungles, climb towering mountains, get involved in politics, lead armies and overthrow empires, and more. The opportunities are endless. One of the many environments ripe for adventure is the open sea, where you can be travellers to distant lands, merchants carrying goods to various ports, or pirates who plunder what the merchants are carrying. Indeed, shipbound adventures can be amongst the most exciting and fun.
Ships of the Inner Sea provides material for gamemasters to use in seafaring campaigns. It describes seven ships that sail the Inner Sea, including details of their layouts, histories, and crews. Some of the ships and crews might be allies of the PCs, or the PCs might even join their crews; other ships contain enemies and villains to fight. All the ships make for interesting encounters, either one-off or recurring. Ships of the Inner Sea doesn't just have to be for seafaring campaigns either. Even campaigns that are mostly landlocked may spend some short periods at sea as the player characters travel from one location to another, and such an occasion could also be a perfect opportunity for an encounter with one of the ships from this book.
I generally like these kinds of sourcebooks as they provide material that GMs can draw on when they need something last-minute, while also being supplements they can build entire campaigns around. For the most part, Ships of the Inner Sea doesn't disappoint. There's a good variety in the types of ships presented and all of them contain enough ideas and adventure seeds to keep any group occupied for some time. It's certainly a resource I will turn to if I run a seafaring campaign at some point in the future.