Three Benchmarks Addressing Open Challenges in Nonlinear System Identification * *We thank Torbjorn Wigren and Per Mattsson (Uppsala University, Sweden) for their help in realizing the cascaded tanks benchmark. This work was funded by the Fund for Scientific Research (FWO), the Methusalem grant of the Flemish Government (METH-1), the IAP VII/19 DYSCO program, and the ERC advanced grant SNLSID under contract 320378. The author J.P. Noel is a Postdoctoral Researcher of the Fonds de la Recherche Scientifique - FNRS which is gratefully acknowledged.