Here is an overview of the full process:
Online tests: these are sent to all applicants as part of the pre-screen - standard CEB/SHL tests, Quantitative + Verbal reasoning
First round interviews: 2 interviews, one with an AC or SAC, one with a Consultant or Case Team Leader. First interview is a pure market sizing + competency, second interview is just one full business case (but if you finish the case early and depending on the interviewer, could also have a small competency element at the end).
Final round interviews: 3 interviews with Managers and Partners. 2 standard interviews with full business case + competency. One interview is a "written case" - you essentially get a pack of information and some questions to solve, and are provided a blank slide deck to fill out. Part of the exercise is math, the other part is making a recommendation based on various facts from the pack.
In terms of location, no interviews are done on campus. First round interviews are either in the London office or over Video Conference if the candidate is too far away (usually outside of Europe). Final round interviews are always in the London office (i.e. Bain will fly you out from wherever you are to attend the interviews).
Hope this helps!