Za'abal Castle, Saudi Arabia

Za'abal Castle is a mud walled castle set on a hill high above the city of Sakaka in northern Saudi Arabia.

The holes in the walls are for firing arrows through but as the walls are made of mud I should think the attackers would do enough damage by using hoses to wash the castle away.

There is a large basin carved out of the rock to catch and store rainwater in times of siege.

I think you'd have trouble dislodging defenders from the castle, but then again why not just leave them there?