  In this paper we show the existence of three dimensional rigid, and thus
unfoldable, lattice conformations. The structure we found has 450+ bonds, and
we provide a computer assisted proof of the existence of such structures. The
existence of such rigid structures illustrates why protein folding problems are
hard also in dimension three. The existence of two rigid two dimensional
structures was shown earlier. This work answers question 8 in \cite{2D} in the
affirmative: rigid self avoiding walks exist in three dimensional lattice
configurations.
