A two-dimensional electron system (2DES) belonging to the InAs conduction band has been prepared by depositing tiny amounts of adsorbates on the InAs(110) surface. Photoemission has been used to determine the resulting 2DES subband energies. Since the 2DES is close to the surface, it could be probed by low-temperature scanning tunneling spectroscopy. In zero magnetic field we find strong and rather irregular corrugations of the local density of states (LDOS), which are interpreted as due to the tendency of a 2DES to weakly localize. Applying a magnetic field leads to Landau quantization and to a dramatic change of the LDOS, which is now composed of drift states running along equipotential lines.