The tube is a manouevre performed in the sport of surfing. When a wave begins to break, it often creates a hollow section as it peels down the sandbank or reef bottom, enabling the experienced surfer to position him / her self in the hollow part of the wave, also known as the tube. The surfer can be completely surrounded by water for several seconds (sometimes much longer depending upon the wave) until the wave forces him / her to exit the tube and go back out onto the open wave face. Given the degree of difficulty experienced whilst riding a tube, surfers often fall off their surfboards before exiting the tube cleanly. Strong tube riding skills can only be acquired from years of experience riding hollow waves and learning to anticipate how the wave will break, thus enabling you to stay inside the tube longer, or exit quickly before the wave collapses on top of you. Some of the world's best known waves for tube riding include Pipeline on the North shore of Oahu, Teahupoo in Tahiti and G-Land in Java, and of course Lanzarotes North Shore. (source Wikipedia)