Different options for proving intense THz filed for THz pump - X-ray probe experiments at the European XFEL using laser-based and/or accelerator-based techniques are currently discussed. Here we present a concept which is based on a superconducting THz undulator utilizing the spent electron beam of the eV scale linac as an afterburner to produce narrowband, tunable, few-cycle THz pulses with world-record intensities. A challenge to this approach is the very high electron beam energy of up to 17.5 GeV which yield particular requirements for the specific undulator design. In this presentation, we will report the preliminary study of the undulator design for the European XFEL and present the radiation properties including expected pulse energies, spectra, and temporal profiles.