The Sargasso Sea Is a Patch of Sargassum Seaweed.

The sargasso sea is the only real sea in the world that doesn't have any land boundaries. It's known for having large rafts of sargassum seaweed within it. The islands can be acres across, while the regions they occupy can stretch for miles. One thing about it is it's known for being a place where ships can easily become becalmed. And this is a risk that people who are not very familiar with sea voyages might not think about very often.