  The weakly bound exotic ${}^{11}$Be nucleus, famous for its ground-state
parity inversion and distinct n+ ${}^{10}$Be halo structure, is investigated
from first principles using chiral two- and three-nucleon forces. An explicit
treatment of continuum effects is found to be indispensable. We study the
sensitivity of the ${}^{11}$Be spectrum to the details of the three-nucleon
force and demonstrate that only certain chiral interactions are capable of
reproducing the parity inversion. With such interactions, the extremely large
E1 transition between the bound states is reproduced. We compare our
photodisintegration calculations to conflicting experimental data and predict a
distinct dip around the $3/2^-_1$ resonance energy. Finally, we predict
low-lying $3/2^+$ and $9/2^+$ resonances that are not or not sufficiently
measured in experiments.
