Ask HN: Suggestions interactive tool for Git history

I have found an undocumented repository (mostly code) that is sufficiently complex; including multiple languages, non-informative directories, no access to original authors, and inconsistent file extensions. It is unclear what the intended scope of the repository is.

Lucky enough, the code base isn't enormous.

I would like to see the git-diff history, as a step by step interface (without getting lost) in an intelligible way.

Does anyone have tool-tips on this?

Also, what other tools do you use to understand such a code base?