Waveguide lattices can be conveniently fabricated by the direct laser-writing with fs-laser pulses. This way a fast prototyping of 3D lattice structures can be realized. Those lattices are an ideal testbed for fundamental quantum physics by studying quantum walks – the propagation of nonclassical states of light through such lattices. This way, photonic quantum simulators can be implemented. In addition, the interaction of a quantum system with an external environment can be precisely controlled, tailored and thus, studies experimentally, thus, allowing new insights in non-Hermitian quantum physics. Moreover, such waveguide lattices offer to implement topological systems which can be probed in the quantum domain to better understand the interplay between topology and quantum coherence.