It's easy to view Monaco as less of a unique challenge in Formula 1 these days, thanks to the opening-up of some of the tight corners over the years and an increasingly super-smooth surface.
But the narrow streets of Monte Carlo and the low-speed, low-energy circuit layout still pose headaches for the teams, which always find different ways to tackle a track that requires maximum mechanical and aerodynamic grip but does not pose the usual downforce vs drag headache.
Most teams brought circuit-specific parts to Monaco, as an extra bit of downforce never goes amiss on a circuit where the penalty you pay for extra drag is less important than at other tracks.