The main body of the bassoon is like all woodwind instruments, a hollow tube. The main tube is made of wood, but there are metal bands around it and metal keys superimposed on it. The bore (the hollow bit inside the wood) is not a cylinder (ie, the same size at the top as the bottom), but is actually cone-shaped. The shape gets wider at the bottom of the instrument (the end furthest from the mouthpiece).
Bassoons come in different sizes, which in length can vary between about 5ft to about 8ft. Even if it were just 5ft, it would be impossibly big to play, so its stretched-out length is doubled back on itself to allow a player to cover the keys with his fingers. Being so big, it has five main sections, one of which is the metal crook.
Then there is the bass (long joint), the bell and the boot (or butt) at the bottom of the instrument. There is also a wing joint that connects the main body of the instrument to the crook (or, as it is sometimes called, the bocal).
Being such a big instrument, the bassoon is played seated, with either a strap around the player’s shoulder, or resting on a spike on the floor. The range of the instrument stretches from the B flat two octaves and a note below middle C upwards for about three octaves.