Riddle: Sally is traveling by ship from south of the equator to the north.
She has a nice little cabin with a bathroom, but no window.
Sally has no compass nor other instruments. Just the
general luggage one brings on board a long cruise. Yet, without
leaving her room or talking with anyone, Sally will be able to
tell when the ship has crossed the equator. How?
Answer: Sally can fill the sink and watch it drain. When the water reverses direction when going down the drain, she will know they have crossed the equator.