One theory is that the Hoover Dam was built by the Freemasons as a secret base. This theory is based on the fact that the dam is built in the shape of a five-pointed star, which is a symbol of Freemasonry. However, there is no evidence to support this claim, and it is likely that the dam was simply built in this shape because it is the most efficient way to design a dam.
Another theory is that the Hoover Dam is hiding a lost city. This theory is based on the fact that there are a number of unexplained tunnels and chambers inside the dam. However, these tunnels and chambers were likely built for maintenance and repair purposes, and there is no evidence to support the claim that they are hiding a lost city.
Finally, there is a theory that the Hoover Dam is a giant water pump. This theory is based on the fact that the dam can generate hydroelectric power, which is a renewable energy source. However, the dam does not actually pump water, it simply uses the power of the water to generate electricity.
In conclusion, there are a number of conspiracy theories about the Hoover Dam, but none of them have been proven to be true. It is likely that the dam is a purely utilitarian structure, and that there is nothing hidden inside it.