In 2014. MAGIC telescopes detected a signal from the gravitationally lensed blazar QSO B0218+357, yielding the detection of the most distant source of VHE gamma-rays ever detected so far by any experiment. Since then, we are still carefully monitoring this source using MAGIC and telescopes sensitive at lower energies. What is there still to learn from this source on the fundamental properties of the Universe?
An introduction about strong gravitational lensing and microlensing, and Multiwavelength astrophysics, will be given in the talk, and ideas for further studies of gravitational lensing effects discussed, such as constraining the sizes of emission regions from AGN at different energies, and testing of gravitational lensing achromaticity.