Quantum fluctuations concerning the shape of nuclei are treated within the framework of covariant density functional theory. Long range correlations beyond mean field are taken into account by configuration mixing of wave functions with triaxial shapes and the restoration of spontaneously broken rotational symmetries through three-dimensional angular momentum projection. The controversial nucleus 16C is treated as an example and it is found that its ground state has a triaxial shape but with large shape fluctuations. They are of crucial importance for a proper description of the spectroscopic properties of such nuclei.