Zeppelins are large airships that use gas, typically helium or hydrogen, to lift off the ground. They have a rigid framework covered with a fabric envelope, which holds the gas. Zeppelins were popular in the early 20th century for passenger travel and cargo transport, offering a unique way to fly. The most famous type of 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, their popularity declined after accidents, such as the Hindenburg disaster in 1937, which raised safety concerns.