How to CTRL + DOWN but based on an adjacent row/column?

Idk how to word it so idk how to search for it. This is a pretty common situation when dealing with missing data. Say I have columns A, B, and A has 599 rows and B has 100, it's missing tonnes of data. Instead of navigating to A1 and CTRL + DOWN, I'm pretty sure there was a shortcut to be in B1 and do the same? I think I accidentally did this once.

I need it because often I start highlighting, say B1, holding SHIFT then DOWN + DOWN + DOWN + DOWN...then realize there's data missing so I want to jump to the bottom of the "table". I can't just add CTRL because that would get me to B1:B100, not B1:B599.