Not as nice as ncdu, but if you have to work with what's already installed:

du -k --max-depth=2 * | sort -rn | head

Ymmv, but playing around with max-depth is usually enough to find the culprit for me.

recently created an alias;

ncdu='ncdu --color dark -q'

-q for quiet, slows updating the ncurses interface down for a quicker scan.

also; -1 for scan info pre ncurses display and -0 for no scan info.

Ncdu is really useful for identifying space hogs.