If $f(x)=18^{x}$, what is $f^{-1}(x) ?$ \[ f^{-1}(x)= \]

Step 1 ：Let's find the inverse of the function $f(x)=18^{x}$.

Step 2 ：The inverse of a function is found by switching the x and y (or input and output) in the original function. So, if $f(x)=18^{x}$, then $f^{-1}(x)$ is found by solving the equation $x=18^{y}$ for y.

Step 3 ：This can be done by taking the logarithm base 18 of both sides of the equation.

Step 4 ：So, $f^{-1}(x)=\frac{\log(x)}{\log(18)}$.

Step 5 ：\(\boxed{f^{-1}(x)=\frac{\log(x)}{\log(18)}}\) is the final answer.