A tourbillon is an addition to the mechanics of a watch escapement to increase accuracy. Conceived by the British watchmaker and inventor John Arnold, it was developed by his friend the Swiss-French watchmaker Abraham-Louis Breguet and patented by Breguet on 26 June 1801.
Here below we can admire a very interesting tourbillon by Le Rhöne watches.
You can see also the difference between a double Tourbillon and single tourbillon.
Different case materials are used for these watches (titanium for the single Tourbillon and rose gold for the double Tourbillon).