  The 3-D structure of the Helix Nebula has been addressed multiple times and
is slowly yielding to application of monochromatic emission line imaging, high
resolution spectroscopy, and photoionization theory. The inner structure of the
nebula is a toroidal disk filled with doubly ionized helium and is ionization
bounded, with an extended vertical component resembling the structure of
numerous bipolar nebulae. The outer structure is less well defined, with one
construction being that there is an open-center outer-disk that is nearly
perpendicular to the inner-disk and an alternate construction that explains the
features seen just outside the inner-disk as being the result of the observer's
line of sight passing through extended lobes perpendicular to the inner-disk. A
definitive model awaits thorough velocity mapping in the major diagnostic
emission lines. However, even our well-defined knowledge of the inner-disk
defies explanation by the simplest application of the broadly accepted two-wind
model for the formation of PN.
