Paris is a city full of well-hidden treasures. Among them is the lake located under the Opéra Garnier. Did you not know it existed? Let’s follow in the footsteps and history of this place that is the source of many fantasies. It was Charles Garnier who imagined it when construction of the building had already started. It is 1861, the work is in progress, but the architect is faced with a big problem: the soil is of very poor quality and the seepage water is so strong that the building could collapse. Several solutions are then considered, including that of constructing the building on stilts. After some thought, we finally decided to opt for a large waterproof tank under the building. Our lake was born! Over the years, many legends have been built around this lake. Some say, for example, that it is fed by an underground river, called the Grange-Batelière. However, if this current of water passes well under the Printemps department store, it bypasses the Opera. The lake is therefore indeed an artificial tank. Unfortunately, this secret remains well hidden in the fifth basement of the Opéra Garnier and we cannot visit it. However, there are living things in its waters. First of all, the carp, which are its permanent residents, as well as the frogmen (firefighters train there regularly)!