We present experimental investigations of tunneling between two quantum wells forming a T-shaped structure. At zero magnetic field we observe a nonlinear tunnel characteristic with clearly pronounced negative differential resistance. With magnetic field B, both quantum wells can independently be set in a quantum Hall state. We demonstrate spectroscopy of Quantum Hall bulk states in one B field orientation, and spectroscopy of edge states with the orthogonal orientation. The observed features can be explained assuming that transverse momentum is conserved during tunneling.