What Were the “Wheels within Wheels” That Ezekiel Saw?

According to most translations of Ezekiel 1:16, the creatures Ezekiel saw included a “wheel within a wheel”. Other translations have the phrase “wheel intersecting a wheel”. (In Hebrew, it's “האופן בתוך האופן”.)

The second translation seems to be nonsense since an object cannot rotate around two different axes at the same time … in three dimensions. Maybe Ezekiel saw a four-dimensional object rotating around two different axes.