Flood an area of the caves.

There's a room in the caves with a few streams that flow into a giant pit in
the center of the room.

Try filling that pit with water.

Some of the streams are fed by dripping stalactites.

Those streams would run faster if the stalactites did more than drip.

Make more water flow out of them.

By opening them up.

Attack them (there are three) with a sword, and the pit should flood.  You
will kill a guard and gain a few items in the process.