In Looker 3.40 we introduced drill menus that allow you to do custom drilling on a dimension. Read more about this here. This includes drill menus in visualizations, allowing you to custom drilling directly from a visualization.
In Looker 3.40, enable this feature by going to Admin > Labs and enabling Drill Menu in Visualizations. In Looker 3.42 and above, this feature is enabled automatically.
To drill from a visualization, click on the part of the visualization you would like to drill into and the menu will appear. From there, you can drill using any options in the menu:
Other uses of drill menus
Read more about: