Are there any airports with multi-level taxiways?
If you allow taxiway to also mean a surface where an airplane rolls but not under its own power, then there's the lower decks of an aircraft carrier, and Schätz's carousel hangars.  Note that even Schätz prefers scissors lifts to multilevel tarmac.
Multilevel tarmac would means ramps between levels, which is commonplace for surface vehicles but rare for airplanes, both in airframe design and in pilot training.