Fast radio bursts (FRBs) are a genuine cosmic mystery: we've studied them intensively for more than 15 years, but we're still not sure what they are. Despite us still not having the whole picture, huge strides have been made in the last few years, thanks to the extraordinary yield of thousands of new FRBs discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). I wll present some of the recent work from CHIME, and will particularly highlight the unique ways in which FRBs are superb probes of gas, magnetic fields, and turbulence along the line of sight.