A zeppelin is a type of airship that is filled with gas, typically helium or hydrogen, to provide lift. It has a rigid framework, which distinguishes it from other airships that are non-rigid. Zeppelins were popular in the early 20th century for passenger travel and cargo transport, offering a unique way to fly above the ground. The most famous zeppelin is the LZ 127 Graf Zeppelin, which made numerous flights around the world. Although they were once seen as a luxurious mode of travel, zeppelins fell out of favor after accidents, such as the Hindenburg disaster in 1937, highlighted safety concerns.