The portion of the story you are referring to is the part
where King Arthur throws his sword, Excalibur, into a lake where the Lady of
the Lake inhabits. After he throws Excalibur
into the middle of the lake and before it lands into the water the Lady of the
Lake catches it and takes it into the lake with her. The Lady of the Lake can be considered a
supernatural being, thus contributing to the supernatural element, an element
which is common in medieval literature.
